Make limited access a bit more useful.

If a user does not have `full_access` then they get a limited view of
the site. This change lets them have a little more by adding Directory
search functionality (with people names only), group and people
messaging, and ability to edit their privacy settings.
Fix bug showing email setting column to everyone.
Fix bug showing the 'Add Someone' box to everyone.
Add back code to throw errors on bad i18n key.
Add indicators when group is linked.
I18n the memberships index page.