Password recovery

[h0pbeat]

We need to add at minimal the link to email with forgotten your password, and implement the proper reset mechanism in the meantime.

[h0pbeat]

Added mailto to login screen for 'forgot your password'.
We should implement proper recovery based on some authentication mechanism (email? student email? phone number? CAS authentication?)

[h0pbeat]

We do the following:

1. Define which fields can be used to send password recovery link/code. To keep things simple, we start with email and support username (=email) and Cas.email
2. When user clicks 'forgot password', we ask him to type in the email and check which email is it. We search username and Cas.email for it.
3. If found, we generate a long token, save it with username, expiration, send email to to the user.
4. When user clicks the link, we check against the objects, and display for the user to type in new password. We set token as used.