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

plugins/win-capture/monitor-capture.c

@@ -138,6 +138,18 @@ static void monitor_capture_render(void *data, effect_t effect)
 	dc_capture_render(&capture->data, capture->opaque_effect);
 }
 
+static uint32_t monitor_capture_width(void *data)
+{
+	struct monitor_capture *capture = data;
+	return capture->data.width;
+}
+
+static uint32_t monitor_capture_height(void *data)
+{
+	struct monitor_capture *capture = data;
+	return capture->data.height;
+}
+
 struct obs_source_info monitor_capture_info = {
 	.id           = "monitor_capture",
 	.type         = OBS_SOURCE_TYPE_INPUT,
@@ -145,6 +157,8 @@ struct obs_source_info monitor_capture_info = {
 	.getname      = monitor_capture_getname,
 	.create       = monitor_capture_create,
 	.destroy      = monitor_capture_destroy,
+	.getwidth     = monitor_capture_width,
+	.getheight    = monitor_capture_height,
 	.defaults     = monitor_capture_defaults,
 	.video_render = monitor_capture_render,
 	.video_tick   = monitor_capture_tick