Airlock controller rewrite

- /datum/computer/file/embedded_program moved from
embedded_controller_base.dm to
code/game/machinery/embedded_controller/airlock_program.dm
- embedded_controller_base.dm cleaned up and identical parts of the
controller subtypes were moved here
- embedded_controller subtypes moved to
code/game/machinery/embedded_controller/airlock_controllers.dm
- Added nanoUI templates for airlock controllers
- Added a couple of classes to nano/css/shared.css for colouring buttons