UI: Use Qt lib for screen info instead of x11 libs

All of the monitor discovery logic can be implemented with Qt. This
change removes all the x11 implementations in favor of Qt and removes a
fair amount of platform specific code.

UI/CMakeLists.txt

@@ -83,19 +83,7 @@ elseif(UNIX)
 	set(obs_PLATFORM_SOURCES
 		platform-x11.cpp)
 
-	find_package(XCB COMPONENTS XCB REQUIRED RANDR REQUIRED XINERAMA REQUIRED)
-	
-	include_directories(
-		${XCB_INCLUDE_DIRS}
-		${X11_XCB_INCLUDE_DIRS})
-		
-	add_definitions(
-		${XCB_DEFINITIONS}
-		${X11_XCB_DEFINITIONS})
-
-	set(obs_PLATFORM_LIBRARIES
-		${XCB_LIBRARIES}
-		${X11_XCB_LIBRARIES}
+        set(obs_PLATFORM_LIBRARIES
                 Qt5::X11Extras)
 endif()