Fix i18n in our browser

Fix i18n in our browser

We only ever served english pages since the switch to werkzeug's requests.
Fix this by actually checking the accepted languages that our web browser
sends and using that or falling back to english.

This is not optimal, imaging our browser sends "klingon, de" as accepted
languages and we happen to not have a klingon translation ready (a deficiency
that should be corrected immediately anyway!!). We would then fall back
to english rather than sending the sensible and pleasant German language
which the user would understand. This will require more backend work though.

Removing the gettext.find() in mg_globals.py. It looked in the wrong directory
anyway (mediagoblin/translations) and as that does not exist, had always returned
None without anyone noticing.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>