Add basic support for MLT GLSL.
Get MLT GLSL working on X11.
Cleanup OpenGL build dependencies on Windows.
Fix deadlock loading second clip with GLSL.
Merge branch 'master' into glsl

Conflicts:
	src/glwidget.cpp
Fix mlt_glsl_texture coordinates with change to GL_TEXTURE_2D.
Fix creating a new audiolevel for each open.
Merge branch 'master' into glsl

Conflicts:
	src/glwidget.cpp
Remove redundant dialog setup lines.
Make GPU processing switchable in settings.

Also, move Settings into its menu of the main menubar instead of hidden
in a context menu.
Fix build on Linux after Settings menu refactor.
Add a splitter grip to Encode dock for Windows.
Fix possible non-return value from PlaylistDock::position().
Fix gpuNotSupported signal connection error on Linux.
Fix player/gpu setting default false.
Fix crash when stop/start consumer with GPU on Windows.
Fixup Mlt::Event lifecycle management in GLWidget.
Remove debug log output.