first attempt at UI rewrite

Full rewrite of browser UI in HTML and javascript/jQuery/AJAX only.  Known issues:
* Autocomplete of opponent name in create_game.html still needs to be debugged, so temporarily using a SELECT for that
* create_user.html/create_user.php not yet migrated
* Some status messages look ugly (but should be logically correct) due to changes in responder.php return values since i started working on this
* On the last attack which ends a game, the UI displays "Received internal error while attacking".  I believe this is a BMInterface.php bug that i'm just passing along, not a UI bug.  The game winds up in the correct logical state after this --- the bug is just the spurious error message.