Configure used languages in TBX-Import

and overwrite languages in the TBX.

Currently translate5 works according to this principles, when importing terminology:
http://confluence.translate5.net/display/BUS/TBX+file+structure

For importing customer terminology it can be necessary, to map the language in the TBX to another language in translate5 (for example to map en-US to en-GB).

This should be achieved by task templates.