Unified Xlib and Xrender font text rasterization

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Removed pixmap creation wrappers in Xlib backend

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Fixed missing color swapping in mem_canvas stencil blending

The stencil blending implementation of mem_canvas did not propperly
swap the colors. As a result, font colors on Windos(R) had the red
and blue values swapped.

Reported-by: Stefan Partheymüller <stefan-partheymueller@gmx.de>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>