Distinguish between banning and rate-limiting

The current automatic blocking that we have only covers rate-limiting
to slow down abuse.

It should be distinguished from outright bans of bad IPs / emails
(which we have yet to implement).
Add a new blockEmail API endpoint

This allows a third-party to ban a given email address for a given
period of time.
Add a new blockIp API endpoint

This allows a third-party to ban a given ip address for a given
period of time.
Always clear everything before the functional tests

We should always clear everything in memcache before running the
functional tests otherwise future unit tests may make them fail.
Make IP and email addresses bans last for 24 hours
Merge pull request #36 from fmarier/ban_ip_and_email

Add new blockIp and blockEmail API endpoints