- Selected but unfocused Source colour
- Scenes font
- Padding when editing Source name

This changes all of the icons from png to svg. With svgs, scaling is
unlimited. With the svgs, the issue of the @ symbols with the Windows
updater is no longer an issue.

I changed the colors of the icons to a light gray (#d2d2d2), in the
dark themes, because I thought they looked better with this color.

The mute, unmute, plus, minus, up, down and expand icons are from the
Feather Icons set. https://feathericons.com/

The visibility icon is from the Octicons set. https://octicons.github.com/

The locked and unlocked icons are from the Open Iconic set.
https://github.com/iconic/open-iconic

- Fixes Q_PROPERTY macro syntax
- Removes excessive notification declaration and slot
- Removes unneeded dynamic property
- Improves Themes versatility

Fixes an issue when it's hard to perform drag-by-mouse move of the
scrollbar while handle is at corner and has minimum size.

Info: the handle minimum size styled as 20px, while add/sub-line is
14px, thus only 6px left for mouse drag when handle resides at corner.
While handle styled to cover whole bar including, subcontrol elements,
it is better to remove the hidden subcontrols completely.

Fixes an issue when it was hard to drag by mouse the scroll handle in
Dark theme if scroll handle size is close to full size
(https://obsproject.com/mantis/view.php?id=466) or close to minimal
size.

Also, the mouse pointer was misaligned to the scroll handle when
moving: the scroll handle always moves faster than mouse pointer itself
and finishes first.

This changes the remux dialog to support a collection of input/output
pairs, presented as a QTableView.  Standard Qt icons are used to
indicate the state of each entry during a remux operation.  Drag/drop
support is added to populate the list quickly.  Both Dark and Rachni
themes are updated to make QTableView look reasonable.

Relevant text is added in the localization files.

Closes obsproject/obs-studio#1153

In the Dark theme, disabled UI elements had text that was too close in
color to enabled UI elements. This commit switches them to use the
"light" palette color instead of the "lighter" palette color.

Adds the ability to set the current palette for the program via adding
"OBSTheme" objects to the qss files.  The values for the OBSTheme object
are the values used by QPalette::ColorRole.

Modifying the global palette allows the ability to easily/quickly look
up application theme colors (especially if you would like to use them
for QML), as well as the ability to fix the hyperlink color issue.  (On
dark themes, links would still be dark blue, causing them to be
difficult to see)

The decay rate of the audio meters can now be selected in the audio
settings.  The values are:

- "Fast"   (OBS default, 40 dB / 1.7s)
- "Medium" (Type I PPM,  20 dB / 1.7s)
- "Slow"   (Type II PPM, 24 dB / 2.8s)

Closes jp9000/obs-studio#1143

Closes jp9000/obs-studio#1141

Closes jp9000/obs-studio#1141

The following features have been added to the audio-meters:
 * Stereo PPM-level meter, with 40 dB/1.7s decay rate.
 * Stereo VU-level meter, with 300 ms integration time.
 * Stereo Peak-hold meter, with 20 second sustain.
 * Input peak level color-squares in front of every meter.
 * Minor-ticks for each dB.
 * Major-ticks for every 5 dB.
 * Meter is divided in sections at -20 dB and -9 dB.

The ballistic parameters chosen here where taken from:
 * https://en.wikipedia.org/wiki/Peak_programme_meter (SMPTE RP.0155)
 * https://en.wikipedia.org/wiki/VU_meter

In the rework I have removed any ballistic calculations from
libobs/obs-audio-controls.c making the calculations here a lot more
simple doing only MAX and RMS calculations for only the samples in
the current update. The actual ballistics are now done by just
the UI/volume-control.cpp because ballistics need to be updated
based on the repaint-rate of the user-interface.

The dB to pixel conversion has been moved from
libobs/obs-audio-controls.c to UI/volume-control.cpp as well to reduce
coupling between these two objects, especially when implementing the
major- and minor-ticks and the sections.

All colors and ballistic parameters are adjustable via QT style sheets.
There are slight differences in colors for each of the themes.

This is to prevent confusion both when prefixing commits and when
reading the directory structure for the first time.

Certain output formats don't support multiple tracks, so it's important
to warn the user if they select multiple tracks.

Also warn the user if they select no tracks.

OBSHotkeyEdit is similar to QKeySequenceEdit, except less terribad on OSX, while
OBSHotkeyWidget provides a container that automagically encapsulates multiple
bindings per hotkey

OBSHotkeyLabel in combination with OBSHotkeyWidget provides mechanisms for
dealing with hotkey pairs (see upcoming usage in window-basic-settings.cpp)

QToolTip's (background) color(s) would not apply on windows, work-around
taken from https://forum.qt.io/topic/24023/

When an item is selected but not focused, it would be too similar to the
non-selected color.

This fixes an issue where the borders for certain types of windows would
not match the intended border style/color.  It was supposed to be 1
through 6 for frameShape, but I ended up putting 5 twice.

Fixes an issue where the border color/style would not be consistent
across different operating systems

Links up certain controls via a "themeID" property so the icons can by
dynamically changed via the qss file if needed.