add Punjbai language (bug 1016125)

https://bugzilla.mozilla.org/show_bug.cgi?id=1016125
this is necessary because we `manage.py update_product_details` will fail during [deployment](https://github.com/mozilla/zamboni/blob/master/fabfile.py#L53-L55) because we get a `KeyError` here because `product_details.languages['pa']` doesn't exist in the local copy of `languages.json`

```py
(z)(driven) %% manage.py update_product_details               /opt/zamboni (pa)
Raven is not configured (logging is disabled). Please see the documentation for more information.
Traceback (most recent call last):
  File "manage.py", line 30, in <module>
    import amo
  File "/opt/zamboni/apps/amo/__init__.py", line 101, in <module>
    import waffle
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/waffle/__init__.py", line 9, in <module>
    from waffle.models import Flag, Sample, Switch
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/waffle/models.py", line 9, in <module>
    from waffle.compat import User
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/waffle/compat.py", line 8, in <module>
    User = get_user_model()
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/django/contrib/auth/__init__.py", line 127, in get_user_model
    user_model = get_model(app_label, model_name)
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/django/db/models/loading.py", line 271, in get_model
    self._populate()
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/django/db/models/loading.py", line 75, in _populate
    self.load_app(app_name, True)
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/django/db/models/loading.py", line 99, in load_app
    models = import_module('%s.models' % app_name)
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/django/utils/importlib.py", line 40, in import_module
    __import__(name)
  File "/opt/zamboni/mkt/abuse/models.py", line 10, in <module>
    from mkt.webapps.models import Addon
  File "/opt/zamboni/mkt/webapps/models.py", line 193, in <module>
    class Addon(amo.models.OnChangeMixin, amo.models.ModelBase):
  File "/opt/zamboni/mkt/webapps/models.py", line 196, in Addon
    do_dictsort(settings.LANGUAGES)]
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/jinja2/filters.py", line 223, in do_dictsort
    return sorted(value.items(), key=sort_func)
  File "/Users/chris/.virtualenvs/z/lib/python2.7/site-packages/django/utils/functional.py", line 125, in __wrapper__
    res = func(*self.__args, **self.__kw)
  File "/opt/zamboni/mkt/settings.py", line 459, in lazy_langs
    for i in languages])
KeyError: 'pa'
```