Implement Kolab 4 rate limitations
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