document PhysicsObjectType constants
document body:FindNearestTo
typo fixes
meh
Properly encapsulate Sector::System.
Defer assignment of faction to Sector::System until first use.
Merge branch 'faction_assignment' into unified_cache

Conflicts:
	src/SectorView.cpp
	src/galaxy/Sector.cpp
	src/galaxy/SectorCache.cpp
	src/galaxy/SectorCache.h
GalaxyObjectCache is now a single template class.