allow players to use keyboard for selecting dice and submitting attacks

* Jenkins: http://jenkins.buttonweavers.com:8080/job/buttonmen-cgolubi1/244/
* Fixes #180 (note: it's possible that #180 encompasses other keyboard navigation that i didn't implement, but this pull implements what irilyth asked for in his bugfix-of-the-month, and IMO people can open new tickets to expand keyboard control to other parts of the UI)