Move startup code to 1 place (#1605)

Created a module to handle all startup and have deploy/unisubs.wsgi
and manage.py call into it.

This should basically result in the same code being run, but there
were a couple changes:
  - unisubs.wsgi: No longer add ../env/lib/python2.6/site-packages as
    a site dir.  I think this is a relic of previous setups.  For
    starters, we're on python 2.7 now.
  - both: set CELERY_LOADER to amaracelery.loaders.AmaraCeleryLoader.
    This is the loader that we want to use and it might have even been
    the one that we were actually using before because we set it up in
    apps/amaracelery/__init__.py