Implement new GST player functionalities

Implement new GST player functionalities

-    seek, setRate, paused, pause, play, didLoadingProgress, networkState, readyState
-    Got rid off static g_player variable.
-    Added async message handler for gstreamer.
-    Removed not used variables/methods.
-    Removed loading ffmpeg libraries.
-    Added startTime attribute for HTMLMediaElement.
-    Added handling of url's with passed parameters (url+"?param").

Change-Id: Iddb87927559029757cc4cfa51d86158ee0fff929

Conflicts:

	src/third_party/WebKit/Source/core/html/HTMLMediaElement.h
	src/third_party/WebKit/Source/core/html/HTMLMediaElement.idl