Add which_lang function

Function allows commands to accept language, blank (all_langs) or
change-id in a reusable way.
Make language code funtion work on Linux and BSD
Enable option_project where needed
Add some default configurations

We'll use these later
Introduce $translation_dir to point to translations
Introduce abstraction of translation file extension

This allows us to work with e.g. .lang files
Add a FIXME for later
Add command to retreive latest change id
Start of generic ttk-build script
Introduce new ttk-build wrapper