More general pushing. Split-down commits are following from now on.
Added ticker to constructor of Corporation
Removed separate Commander storage from Fleet
Removed separate commander storage from database as well
Renamed "corp_id" to "corporation_id" in corporations table
Added LoadCorporation and LoadPlayer to Database
Change the Fleet and FleetMember "constructors" to include all parameters of the objects
Changed AddMember of Fleet to expect a FleetMember object (does not appear to work though)
Changed all "constructors" to return pointers instead of objects to avoid issues with passing them around
Added loading of FleetMembers and Fleets to Database