obs-filters: Use double-precision where viable

libobs: Copy metadata for tracks/streams when remuxing

Allows the ability to group scene items.  Groups internally are
sub-scenes, which allows the ability to add unique filters and
transforms to each group.

Allows scenes to have a custom size.  Mainly used for grouping, but can
be extended with public API later.

Prevents a potential race condition with the scene mutex.

Defers updating the scene item transform to the graphics thread to
reduce the number of transform update calls.

Fixes a bug where items that had cropping would recalculate transform
every frame.  obs_scene_item::last_width and obs_scene_item::last_height
would be set to the cropped sizes rather than the source's actual size.

Adds a simple signal reference counting function
(signal_handler_connect_ref) that makes it so that signals keep the
handler around until the all the signal itself is disconnected.  This
prevents potential crashes where a signal might try to disconnect after
a handler has already been destroyed (typically in C++ with
OBSSignalHandler helper objects, where destruction isn't guaranteed to
be predictable).

This also modifies OBSSignalHandler to use the reference-counting
connections.

Allows using obs_scene_add_internal to add without sending signals.

We're expecting a variable with double precision. Since we don't read
the value of these doubles with a particular precision, it can often
lead to unpredictable results where the value set isn't the one
intended due to the loss of precision from float->double conversion.

Windows 10 shows a busy cursor when a process is created, this is not
useful for our background processes which have no UI.

Closes obsproject/obs-studio#1300

CI: Upgrade to VS2017 on Appveyor

Multiview updates

The variable name changes were done with the intent to ease the
abstraction of the scene, preview and program width/height size
so its not related with the canvas size but directly related with
our concept of scenes.

The variable name changes were done with the intent to ease the
abstraction of the scene, preview and program width/height size
so its not related with the canvas size but directly related with
our concept of scenes.

Make the safe areas respect the EBU R 95 and Rec. ITU-R BT.1848-1
standards for 16:9 content.
Links: https://tech.ebu.ch/docs/r/r095rev1_March2016.pdf and
https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1848-1-201510-I!!PDF-E.pdf