Tests: added Arabic language fixture
Tests: allow passing options when creating projects
Tests: added disabled tutorial project
Tests: added disabled TP
Tests: check `get_path_obj()` behavior
TranslationProject: added convenience `disabled()` manager method
Removed unnecessary MySQL-style quoting
Take into account TP state when querying cross-language resources

Both Store and Directory queries were not taking into account the state of
projects and translation projects, thus leading to incorrect overview
listings.

Fixes #167.