add tests for django 1.7
travis and django 1.7
django 1.7 compatibility

 * deprecations : get_query_set, model.module_name
 * app loading : must use some late imports and introspection
 * settings : default middlewares changed
 * metaclasses : copy updated method from six for django 1.5 to 1.7 compatibility
 * Tests for other versions still pass.
documentation update for django 1.7
travis and django 1.7rc2
more output from travis
compilemessages must be called as command
Merge branch 'django1.7' of https://github.com/NotSqrt/django-parler
finetune Django 1.7 compatibility checks