Command Interface [WIP]

* Basic Interface:
    - Supports starting specific task and last active task.
    - Supports stopping specific active task or most recently activated
      task.
    - Receive recently used tasks with result offset and count limit.
    - Server pushes updates to clients so they can sync without polling
      constantly.

* TCP server glue added.
    Binds to 5323 by default, supports multiple clients.

* Local socket server glue added.
    Binds to /tmp/charm.sock on Unix, supports multiple clients.

Change-Id: I8da8b11d45a294ac2f78a181ecaa6debba9c6f50