WOAT: Store PGP keys in DNS

Summary: Added some tests and comments

Test Plan: ./phpunit --testsuite=Unit,Feature,Functional

Reviewers: #hkccp_developers, vanmeeuwen

Reviewed By: #hkccp_developers, vanmeeuwen

Subscribers: vanmeeuwen, #hkccp_developers

Differential Revision: https://git.kolab.org/D2882