Lease & Leadership Functionality

To assist with understanding this code, have a look at the [spec](https://drive.google.com/open?id=0B24olKDYt1DQa1piUFhSMGpuWjA&authuser=1) ([here for commenting](https://drive.google.com/open?id=12Y65IYFNOy9VwjpBrlKHP5XTek1vRYQ5VJSk0L8xbTQ&authuser=1)) -- specifically the diagrams outlining the different layers.

At a high level, this branch introduces a lease service which other systems will be utilizing -- the first of which is also in this branch: the leadership service. Please read the spec for more background information.