Migrate destination handler for Rooms bookable unit entities.
Generalized rooms unit base migration class for csv import.
Merge pull request #31 from peterlozano/MigrateRoomsUnit

Migrate destination handler for Rooms bookable unit entities.
Make unit_csvcolumns static and remove unneded code.
Clean up code comment.
String overhaul: use t() to translate unit type labels
ROOMS-16: Clean up text