Keep contact address on file for accounts

[adehnert]

It would be useful for a couple reasons to have email addresses on file for lockers. signup could prompt for this information and store it in LDAP, and then pony could allow further changes.

Uses of this data could include:

• reporting compromised apps
• reporting upgrade failures of apps
• possibly automatically poking people whose apps are generating a lot of error_log spew
• subscribing users to scripts-announce or informing certain users (old Mediawiki's, say) of upgrades

There's also a question of how to initially populate the database, though I think that should be out-of-scope for this ticket.