[bug 834279] Add persona authentication

Adds persona support for logging in. It's set up such that it doesn't
create new accounts. Accounts must be created manually by an admin.
Nix unused import
Add TODO for removing stubs
Put browserid.js file in bundle; fix site_js block inheritance

* move browserid.js to the base bundle
* change the dashboard templates to inherit the site_js block
  from base.html
* attempt to add comments that explain what's going on so it makes
  sense to future developrs
Fix missing gettext calls
Nix home-view
Add troubleshooting doc and tweaked local.py-dist

This will theoretically alleviate issues with setting the site up for
functional persona auth for future people.