Moves /obj/machinery/turretid to its own class/file.
Nabs /tg/ support procs and defines.
Moves down target assessment into machinery.
Ports /tg/'s portable turrets.

However, skipping porting /tg/'s projectile system for now. Not going to swallow more than I can chew here.
Replaces the normal turrets with the new porta-turrets.
Fixes a bug with stationary turrets. Removes quotes in path-name to ensure type always exists. Includes code review suggestions.
Merge remote-tracking branch 'upstream/dev' into PortaTurret
Merge remote-tracking branch 'upstream/dev' into PortaTurret
Merge remote-tracking branch 'upstream/dev' into PortaTurret
Merge pull request #6835 from PsiOmegaDelta/PortaTurret

Portable turrets update