Add (temporary terrible) volume controls

- Add volume control

   These volume controls are basically nothing more than sliders.  They
   look terrible and hopefully will be as temporary as they are
   terrible.

 - Allow saving of specific non-user sources via obs_load_source and
   obs_save_source functions.

 - Save data of desktop/mic audio sources (sync data, volume data, etc),
   and load the data on startup.

 - Make it so that a scene is created by default if first time using the
   application.  On certain operating systems where supported, a default
   capture will be created.  Desktop capture on mac, particularly.  Not
   sure what to do about windows because monitor capture on windows 7 is
   completely terrible and is bad to start users off with.

obs/CMakeLists.txt

@@ -59,6 +59,7 @@ set(obs_SOURCES
 	window-basic-properties.cpp
 	window-namedialog.cpp
 	properties-view.cpp
+	volume-control.cpp
 	qt-wrappers.cpp)
 
 set(obs_HEADERS
@@ -71,6 +72,7 @@ set(obs_HEADERS
 	window-namedialog.hpp
 	properties-view.hpp
 	display-helpers.hpp
+	volume-control.hpp
 	qt-display.hpp
 	qt-wrappers.hpp)