Added Mechanics workshop to Taxistation.

Replaces the slightly defunct Taxi office. Also expanded podbay slightly for extra space for the fabricator and parts. Spawning works correctly in testing. This is on the engineering station, so it won't have to be moved if the job ever is.

![new taxi workshop](https://cloud.githubusercontent.com/assets/7339857/5149993/5a40e714-71c6-11e4-9c0a-3be4553e939b.PNG)

Should now also be updated to all new pathing.
Old references to obj/machinery/hydroponics over obj/machinery/portable_atmospherics/hydroponics should be gone, as well as other defunct paths.