Add comparison functors for SystemPath to compare by sector only and by system only.
Extract templated base class from SectorCache.
Rename SectorCache.* to GalaxyCache.*
Don't assume that the master cache is the global cache.
Rename Sector::GetSystemPath to Sector::GetPath.
Derive StarSystemCache from GalaxyObjectCache template.
Add a finish callback for cache filling.
Update StarSystem cache when switching spaces.
Galaxy cache usage statistics.