Make dummy MVD client optional (server side).

Add ‘sv_mvd_spawn_dummy’ variable. Spawn dummy client by default only
when game mod advertises support for MVD.

Fix a memory leak when dummy MVD client is rejected by game mod.

Properly push the last server command sent to all GTV clients before
they are dropped due to fatal error or server shutdown.
Make dummy MVD client optional (client side).
Mark more makefile targets as phony.
Fix scaled Player Setup menu drawing.

Restore custom 2D rendering parameters (clip rect and scale) after
rendering 3D view.