Implement Kolab 4 rate limitations

Summary:
This change moves policy maintenance wrt. rate limitations to Kolab 4, with
a policy that with >= 10 messages per hour, or >= 100 recipients per hour, blocks further delivery of email.

Another magical threshold of 2.5 times those rates will automatically suspend the account.

Test Plan: ./phpunit

Reviewers: #hkccp_developers, machniak

Subscribers: machniak, mollekopf, #hkccp_developers

Differential Revision: https://git.kolab.org/D3161