SEPTA: Add aliases for some train stations.

SEPTA's API uses some non-intuitive and inconsistent names for stations. I ran into this frustration over the weekend.

This PR adds some aliases for common stations to make triggering the IA more natural.

Other changes included:

 - Added abstract to SEPTA.pm

 - Changed one of the previous tests to use `49th st` instead of `49th street`, which was not a valid station name.