minimap: initial support
minimap: tidy the transform code a bit, background color and zone dependent scaling
renderers: add ScissorSet and ScissorEnable

Used to control temporarily glScissor, the scissor is also modified
by other parts of the renderer.
Adapted from a commit from `Ishq (ded55d8f12e03aceff) + fixes
cgame: Add scissoring support
minimap: use scissoring to keep the map in the canvas
minimap: add DrawMinimapObject, rework transform and add player arrow
minimap: show teammates, first version
minimap: use the center of the image bounds as it's 3d origin
minimap: add cg_drawMinimap, globalScale and bgColor alpha
renderers: finish sending commands before changing the scissor state
minimap: add cg_minimapActive for HUDs and implement teammates with fading
renderer: fix backport of a rendererGL fix
minimap: move code around for clarity, functionaly equivalent
minimap: try to show the same region for everyone, more const
Merge branch 'minimap'