Add source properties window (very preliminary)

 - Add a properties window for sources so that you can now actually edit
   the settings for sources.  Also, display the source by itself in the
   window (Note: not working on mac, and possibly not working on linux).

   When changing the settings for a source, it will call
   obs_source_update on that source when you have modified any values
   automatically.

 - Add a properties 'widget', eventually I want to turn this in to a
   regular nice properties view like you'd see in the designer, but
   right now it just uses a form layout in a QScrollArea with regular
   controls to display the properties.  It's clunky but works for the
   time being.

 - Make it so that swap chains and the main graphics subsystem will
   automatically use at least one backbuffer if none was specified

 - Fix bug where displays weren't added to the main display array

 - Make it so that you can get the properties of a source via the actual
   pointer of a source/encoder/output in addition to being able to look
   up properties via identifier.

 - When registering source types, check for required functions (wasn't
   doing it before).  getheight/getwidth should not be optional if it's
   a video source as well.

 - Add an RAII OBSObj wrapper to obs.hpp for non-reference-counted
   libobs pointers

 - Add an RAII OBSSignal wrapper to obs.hpp for libobs signals to
   automatically disconnect them on destruction

 - Move the "scale and center" calculation in window-basic-main.cpp to
   its own function and in its own source file

 - Add an 'update' callback to WASAPI audio sources
Initialize properties with current settings

I neglected to make it initialize the actual control values with the
current settings
Add properties to osx display capture

Also add support for capturing displays that are not the main display as
preparation for moving the code from test-plugins into a proper plugin
in the future
Add per window GL context for Cocoa libobs-opengl implementation

This fixes some problems with multiple swap chains (e.g. flickering
between the render views)
Release IOSurface only after it is no longer in use (e.g. by a texture)
Implement encoder usage with outputs

 - Make it so that encoders can be assigned to outputs.  If an encoder
   is destroyed, it will automatically remove itself from that output.
   I specifically didn't want to do reference counting because it leaves
   too much potential for unchecked references and it just felt like it
   would be more trouble than it's worth.

 - Add a 'flags' value to the output definition structure.  This lets
   the output specify if it uses video/audio, and whether the output is
   meant to be used with OBS encoders or not.

 - Remove boilerplate code for outputs.  This makes it easier to program
   outputs.  The boilerplate code involved before was mostly just
   involving connecting to the audio/video data streams directly in each
   output plugin.

   Instead of doing that, simply add plugin callback functions for
   receiving video/audio (either encoded or non-encoded, whichever it's
   set to use), and then call obs_output_begin_data_capture and
   obs_output_end_data_capture to automatically handle setting up
   connections to raw or encoded video/audio streams for the plugin.

 - Remove 'active' function from output callbacks, as it's no longer
   really needed now that the libobs output context automatically knows
   when the output is active or not.

 - Make it so that an encoder cannot be destroyed until all data
   connections to the encoder have been removed.

 - Change the 'start' and 'stop' functions in the encoder interface to
   just an 'initialize' callback, which initializes the encoder.

 - Make it so that the encoder must be initialized first before the data
   stream can be started.  The reason why initialization was separated
   from starting the encoder stream was because we need to be able to
   check that the settings used with the encoder *can* be used first.

   This problem was especially annoying if you had both video/audio
   encoding.  Before, you'd have to check the return value from
   obs_encoder_start, and if that second encoder fails, then you
   basically had to stop the first encoder again, making for
   unnecessary boilerplate code whenever starting up two encoders.
Add dummy GL texture flag & direct object access

 - Add dummy GL texture support to allow libobs texture references to be
   created for GL without

 - Add a texture_getobj function to allow the retrieval of the
   context-specific object, such as the D3D texture pointer, or the
   OpenGL texture object handle.

 - Also cleaned up the export stuff.  I realized it was all totally
   superfluous.  Kind of a dumb moment, but nice to clean it up
   regardless.
Minor fix to GL texture cleanup

Don't clear any data if it's a dummy texture.
Fix CMakeLists.txt for each project (my fault)