Provide read and overwrite for Lisk counters

Summary:
Ref T6881. This is part 1 of my 35-step plan to support subscriptions that bill monthly.

Expanding the capabilities of counters will let me use them to create a logical clock on time-based event updates, build a daemon on top of that, and eventually get time-based triggers.

Test Plan: Added and executed unit tests.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: chad, epriestley

Maniphest Tasks: T6881

Differential Revision: https://secure.phabricator.com/D11395