use default search title from speeches app
link in green instance header to edit instance details
remove almost all of the user dropdown menu
Allow sharing of instances with collaborators.

Create a share instance page with a box to enter an email address.
If we know the email address already, add it to the instance.
For unrecognised emails, create a user with that email and add to the instance.
If the email address is short enough, it'll be used as the username, otherwise,
we use a portion of a hash of it instead.

In either case, redirect the sharer to a confirmation page on success.

The new user gets sent an email inviting them to contribute to the sayit
instance, which a link to follow at which they can set a password and then
be redirected to the instance home page to join in with curating it.
Require user logged in to the correct instance to invite others.
Use correct instance domain in invite accept link.
Log the user in when they accept an invite.