Links many map-specific details such as the station name, z-level information, and allowed jobs from global vars to map datum vars, which should help us maintain multiple maps at once in the future, which will be needed for the future Southern Cross.
Note that a config change will be needed to change GENERATE_ASTEROID to GENERATE_MAP, otherwise no changes should be required to continue normal map usage.
To change to a different map, it's suggested to tick the file that ticks all the other needed files, which for the Northern Star is called northern_star.dm.
No mechanical changes come of this change, only the ability to have an antagonist faction, as well as having specified visbility for the affiliation itself.
Also adds Skrell home system to the home system list.
Makes the name of the starsystem and station generic such that it can be modified in global.dm and replace the strings where it is used. This won't have an effect on Polaris itself, but makes changing the name much more simple for forks. Using string concat constants on the advice of Psi.
