[[ RefactorGraphics ]] add MCContextCopyImage function
[[ RefactorGraphics ]] refactor to use MCGContextCopyImage() when creating new images
[[ RefactorGraphics ]] move libgraphics & libskia dependencies to kernel target.
Add libgraphics & libskia to linked libraries of standalone, server & installer targets
[[ RefactorGraphics ]] add new graphics source files to server target. add srvtheme.cpp with MCThemeDraw() function
[[ RefactorGraphics ]] update metacontext lock/unlock to return a MCGContextRef
[[ RefactorGraphics ]] update tilecache snapshot to use MCGRaster