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

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

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.

Code refactorization. VBO_CONTAINER is split to [NON]CACHED_MANAGER, GPU_MANAGER and VERTEX_MANAGER.

Removed most of deprecated OpenGL calls. Items used to be drawn in immediate mode now are drawn using vertex arrays.

Fixed drawing stroked semicircles using OpenGL backend.

VBO_CONTAINER: Changed new[]/delete[] pairs to realloc(), possibly reducing memory fragmentation and the container shrinking time.

Faster circles & semicircles drawing for the shaderless OpenGL backend. Removed unnecessary variables and computations.