Allow unspecified player and button at the level of the back-end

This pull request addresses the back-end requirements for #75 (unspecified opponent) and #185 (unspecified button).

Currently, the validation of new games is unchanged, which should theoretically make this pull request invisible to users. There are extended comments in Newgame.js to indicate how to loosen the validation requirements to allow for an unspecified opponent and/or button.

Requires database update 00075_empty_name_01.sql

http://jenkins.buttonweavers.com:8080/job/buttonmen-blackshadowshade/203/