Attempt implementation of robot chat.

I updated the description of the /spawnrobot command in the mod's yaml file. I also added a shell script in the proto file to build the java classes - although I was unsure why this didn't exist already. Should maven be doing that? I have been unable to test whether the chat implementation works because I have been unable to successfully run the mod (even your original from the master branch) on my local spigot server. I can build the mod and load it, and spawn a robot pumpkin and give it commands from within the game - however when I try and connect using a python script (e.g. <code>rob = Robot("Normangorman", "localhost")</code>) the server immediately crashes with an error message I can't understand. The full server log can be seen here: https://gist.github.com/Normangorman/adc866a18d96c80f2750

My implementation of the chat method currently will always send a private message to the robot's owner. The next step I think is to increase the functionality to allow either a private message to the owner or a public chat message.

I would be very grateful if you could review my changes and also suggest why the mod is crashing on my server :)