Classic overhead run-and-gun game

Options in pause menu and misc features / bug fixes

Fix crash when continuing game
Fix ammo pickups for dropped grenades
Fix crash in Most Classified Enemy campaign
Fix crash when player has no melee weapon
Fix crash when freshly installed game generates invalid config #839 (reported by @reinerh)
Fix compass arrows slightly off direction #836
Add options in pause menu #284
Add --listen_port N command option for specifying network port #840 (requested by @reinerh)
Improve UI with flashing elements when certain things happen like getting hurt or picking up items #678