Layout for upgrade banner configuration

Show the two banners side by side in wide viewports, stacked in narrow.
Upgrade to latest django-browserid, including removing six.

Six is no longer required by django-browserid. :D
Integrate latest django-browserid.
Fix bug 1005124: Allow inline JS on referral view.
Bug 1005164 - add "how it works" to dashboard

Also updated home page graphic
Add pontoon to CSP styles whitelist.
Localized category and banner names.
Fix bug 1005913: Add a fallback to link referral for no-JS users.
Add pontoon to CSP image whitelist.
Prefixes over new databases because policies go go go.
Remove upgrading docs.
Fix pluralized translation bug by not pluralizing on a string.
Add Google Analytics to base template.
Customize Persona popup.
Use funfactory's reverse across the site for locale-aware URLs.
Add -q flag to nightly_update.sh to silence non-error output.

This includes silencing warnings and non-erroneous logging from 
django-browserid along with updating the commands to accept the -q 
parameter.
Cut down unnecessary queries via prefetching.
Update to latest django-cache-machine.
Hook models up to django-cache-machine.

The mixin and manager don't quite work when you inherit them, so we 
can't just add them to ModelBase. Oh well. :(
Fix bug 1007842: Mark banner size HTML as safe on link detail page.