[refactor] Extract calling *_start to method
Remove unused empty methods
Defer fetcher instantiate

Don't instantiate when not needed.
Useful for inheritances.
Let villein.gem path customizable
Delegate #*? methods to Logger
Add Mamiya::Master with minimal implementation

- Mamiya::Master inherits Mamiya::Agent
  * Removed support of Mamiya::Fetcher
  * Starts Mamiya::Master::Web rack applicaion for API
  * Limited events to handle

- Mamiya::Master::Web
  * Simple sinatra application

- `mamiya master` command to start Mamiya::Master