Allow leases to be explicitly released via web or CLI

Summary: Permit the forcible release of Drydock leases. The implementation isn't very exciting for now.

Test Plan: Released leases via web and CLI.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D4181