Introduce OpenGLContext::MakeCurrent for switching between contexts

Change-Id: I00b06d1330241c4df3b07dc6e0019c49fd7aa521
OGLWindow: set pos and size values even it is invisible

Change-Id: I10392d744bbfe3c4d3f44ff9ca53ff12a2c41c45
OpenGLContext: destroy context

Change-Id: Ia779045d93361a4ca4bfe5027958a04fdebd2ca1
avmedia: make OpenGL window render model when play button is pushed.

Redraw player window (call update) when Paint() is called on its
parent.
Use a temp variable to save playing state.

Change-Id: I3d9b716c7f77587d98e4c06dca6d43a7dc8e32dd
Slideshow: display OpenGL window also during slideshow

Use vcl based player window initialization.

Change-Id: If5c2198fa891e1d3ad218c8b7e1495161c0d6c25