This introduces the OBSSignals data role, which will be used to store
signal handlers in stock Qt objects

This filter simply modifies the volume of the signal as a convenient way
of modifying the volume before other filters, or amplify the volume
without having to mess with advanced audio properties.

This adds functions specific to audio math, which at the moment is just
converting to and from decibel and multiple.

These functions are already defined in math.h, so there's no need to
define them again.

Use the config button on volume controls to allow the ability for
filters/properties to be accessed via the mixer.  Particularly useful
for the purpose of accessing filters/properties of global audio outputs
that are added via audio settings.

This simply saves/loads the actual list widget item order.

The reason why this is done is because internally, libobs doesn't have a
list of scenes, it only has a list of sources.  The list of scenes is
actually something artificially implemented by the basic window user
interface.

The item in the [Output] section for the output mode is "Mode", not
"Type".

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.

If the recording format is unsupported or doesn't support multiple
tracks, warn the user to check their settings.

Add a listboxes to recording to allow changing file formats (allows mp4,
mov, mkv, ts, flv)

This allows the ability to save different container formats, such as
mp4, mkv, and ts files.

In addition to the flv file format, this allows the ability to save to
container formats such as mp4, ts, mkv, and any other containers that
support the current codecs being used.

It pipes the encoded data to the ffmpeg-mux process, which then safely
muxes the file from the encoded data.  If the main program unexpectedly
terminates, the ffmpeg-mux piped program will safely close the file and
write trailer data, preventing file corruption.

This allows an output to specify that the format or track count is
unsupported.

Allows obs-encoder callbacks to remove themselves while in a callback.

Allows audio-io callbacks to remove themselves while in a callback.

The size parameter is the size of the elements, not the size of the
data.  The size parameter should be 1, and the elements should be the
number of bytes.

The reason why I'm making this change is because the fread/fwrite would
fail when the parameters were swapped.

When the editable list property was added, I added a case to a switch
statement without putting a break on the case before it.

This is mostly so that it can be used with the scroll filter, which uses
identical shaders, but needs to wrap the texture instead of clamp.

You should really auto-update these lists from Twitch API.

Closes jp9000/obs-studio#440