Add remote lock

[dfarr]

See the api specification here.

We will need to extend our ILock interface to include a timeout parameter on the tryAcquire function. This parameter can simply be ignored in the local lock implementation.

Unlike local locks, remote locks will require a heartbeat. The heartbeat can be implemented behind the ILock interface in a control loop, let's just make sure that the heartbeat interval is (well) smaller than the timeout interval.