Added a scheduler to check if port is open, and initialize panel

Also:
- Changed the byte order of pixels sent to the Arduino.
- Fixed double listener registration.
- Added TODO.
Use a deque for the pixel queue

Also added...
confirmed: true after first pixel acknowledgement received
waiting: waiting for acknowledgement after sending a pixel
Split up Jumbotron into separate classes

About time too. Much more manageable now.
Added "/jumbo refresh" command

Now you can manually refresh the pixel grid using a command.
Added config.yml

World and screen parameters are now set in a config file, as well as the
Arduino's com port and retry interval in seconds.

If no valid world is specified the plugin will gracefully exit.