Minor functionality updates

1. Added support for init(). So a module can control if agent is to be started for the given arguments and previous data.
2. Updated method arguments. Passing a handler object to fetch older records only if required.
3. Fixed agent initiated message to appear only after an iteration is completed.
4. Changed init command to start and destroy command to stop.
5. Updated README with the new updates.

Core Layer for watch-agent

1. Supported commands init, destroy and show
2. Added suppot foe three method implementations fetch, infer and display which are called implicitly when the commands are called.
3. Storing data in .json files of ~/.watch-agent folder for each module