Made the 'Volunteer' button always visible.

Previously, the volunteer button was only visible when a user was
signed in. Now, it is always visible; if the user is not signed in,
they are presented with the login dialog.

Fixes #259
Adding translations for more volunteer modal fields.
Merge pull request #402 from DavidEBest/devel-alwaysshowvol

Made the 'Volunteer' button always visible.