Making celeryd consistent: look for mediagoblin_local.ini

Use mediagoblin_local.ini as default conf file if it exists, else use
mediagoblin.ini, just like everything else.
Translate form validation error messages.

Okay, this is a long story.
There are two ways to translate validation error messages:

1) Let wtforms do it. You give wtforms a translation thingy
   and it calls it for the message to be translated. Good
   idea maybe. Except: The translation function is only
   called for the builtin messages of wtforms. It's not
   called for any handcrafted messages in the constructor.
   And we can't translate the message there! Because the
   message needs to be translated when the form is
   rendered, for each user's locale.

   This does not work for us.

2) Translate the message while it gets rendered.
   Luckily we render the message completely by hand. So we
   can just translate it there also!

   Simple, easy, works!

This all does not cover translating the builtin messages of
wtforms. They're currently not extracted in any way, so our
translators can't translate them.

But that's another issue!
Removing mongo and mongokit as dependencies.
Removing wipealldata command and deleting env_export/env_import for now.

None of these tools really work anymore in the SQL world, and possibly
aren't as necessary either.  In the meanwhile, just disabling them to
reduce confusion.
Deprecate ./bin/gmg migrate.

Keeping it around just in case someone manually wants to migrate
before running the convert thing or... something.  Probably silly.
No need to keep around mongodb migration tests.
Removing references to MongoDB in docs/
Committing present MediaGoblin translations before pushing extracted messages
Committing extracted and compiled translations
./bin/gmg migrate -> ./bin/gmg dbupdate in the docs
Also tell people to install python-psycopg2 if using postgres in docs
0.3.0 *is* released!  Reflect that in the release notes :)
One character chage: "our" to "your" in the release notes as it makes more
sense, I believe.
Update version to 0.3.0 for release
Update version to 0.3.1.dev
A couple of typos in docs... MedaGobilin->MediaGoblin
Apparently I can't correct typos right.  MedaGoblin->MediaGoblin in docs
gandaro points out we should have all headers end with question marks for consistency

Done for about.rst
Added logging to meddleware.csrf
401. Plugin infrastructure

* implements installing, loading and setup for plugins
* codifies configuration
* has a sample plugin
* docs
* tests