UI invokes responder.php as /api/responder

* Fixes #228 (though this turned out to be trivial because apache does all the hard work in its default PHP configuration, and redirects /api/responder to /api/responder.php)
* While i was at it, moved the guts of responder and dummy_responder to their own class files and gave them camelcase class names, taking care of 4/6 of the remaining checkstyle issues
* While i was at *that*, double-checked that PHP unit tests still pass in vagrant and jenkins if i remove those vestigial requires from BMInterface.php and BMDie.php, and that i can still play a game.  With that, we have zero checkstyle warnings, making it easy for us to be alarmed if we see any again in the future.
* So those things partially address #417
* Jenkins: http://jenkins.buttonweavers.com:8080/job/buttonmen-cgolubi1/128/