Moved the SectorCache out of SectorView so it can be used elsewhere like LuaStarSystem.
Use the sector cache everywhere possible.
Merge remote-tracking branch 'fluffyfreak/sector-cache' into sector-cache
convert SectorCache to object
move SectorCache into libgalaxy
don't expose the internal cache object
always require a SystemPath for GetCached

most of the time we already have one, so no need to decompose it every time
Merge branch 'sector-cache'