Moved background color settings from GAL to RENDER_SETTINGS. Added RENDER_SETTINGS::TranslateColor() to convert between EDA_COLOR_T and COLOR4D.

Screen size is saved in VECTOR2I instead of VECTOR2D.

Corrected the error message about required OpenGL version for GAL. Fixed pcb_calculator .desktop file.

Removed a few RecacheAllItems() calls, some of them changed to specific type recaching (using TYPE_COLLECTOR & VIEW_ITEM::ViewUpdate() ).
Removed OPENGL_GAL::SetStrokeColor().

Changed the used framebuffer object extension from ARB_framebuffer_object to EXT_framebuffer_object (compatibility reasons).

template<> -> template <>
Some more reformatting according to uncrustify results.

Added flipping mode.

Smarter way of the overlay rendering (overlay is always refreshed, while cached&noncached targets only if the viewport or items have changed).

Fixed blending function for OpenGL compositing. Corrected documentation, removed unnecessary functions.