Make conversion of bitmap from OpenGL render context to WPF image more stable.
Merge pull request #48 from robinsedlaczek/Issue44

Make conversion of bitmap from OpenGL render context to WPF image more s...
Unregistering OpenGlControl's events when i'is removed from visual tree, to allow GC to clear memmory and stop rendering loop.
Merge branch 'master' into v/2.4