Views and tests for Invite New User

[Paul Everitt]

Implement the view, template, and tests for invite-new-user, including:

1) The template for the mail that goes out with the invitation.

2) Using IMailer to generate the mail.

3) Create an Invitation object stashed away in the community['members'].invitations.

4) Tests for invitations.

Some random requirements:

1) If an email already maps to a known user, don't re-invite them.

2) Keep track of how many invitations were sent and how many existing users were invited, and put said information in the status_message on the URL when redirecting to manage-members.

3) Handle form validation if there is an email-address that looks malformed.

[Paul Everitt (paul-agendaless)]

Initial work done by Paul.