Move Warp's CommandService to Protocol

Warp provides a very nice SPI for running commands remotely. I would love to see this this SPI become part of the Protocol classes, making it available to all Arquillian code. I'm writing an extension, which needs to execute some code in the container, but is triggered on events fired on the client. Warp's CommandService would allow me to do this, but it only works in Warp tests, which my tests are not. Also, making the code part of Protocol should remove quite some duplication between Protocol and Warp's CommandService.