Added hooks for server: USE THE POWERUP GET/SETers

We get bad server/client desyncs if you directly alter doomBeamNum or
doubleShotNum. You can access and check the value, but you can't change it
yourself. Use powerupxxxxUsed(num) and powerupxxxxGained(num) to
decrease/increase the number.
Merge branch 'master' of https://github.com/cdelguercio/f2pgame