Add email matching on sign up to existing person_id

Not hooked into any backend functionality, but user's email
is checked against emails of people and person_id is set if
the user confirms.

Matching person avatar could use styling. It's HUGE!!!

#18
Update gems & modify code as necessary

Closes #49
Add identity model and mailer WIP

#18
Add email matching validation for identity

#18
Add identity creation at registration when person

#18
Add authorization based on roles for identity

#18
Add identities_controller#update for state change

This is just the controller action for processing. Still needs button
on users#show when staff member.

#18
Move from Role to UserRole to avoid name collision

Person model instances may have data come that under the
attribute name roles which was causing problem. Switch fixes
it.

#18
Add staff member email notification of identity

#18