Progress towards AJAX version

Significant progress. The message now updates without reloading the page
when submitting from the bootstrap element. Some things that still need
to be done:

-- We should return JSON rather than text so we can indicate when the
   game is over and hide the input box.
-- We need to tweak the input so pressing ENTER also submits.
-- We need AJAX-based "Surrender" and "New Game" links.
Send JSON over AJAX

We now send JSON as a response to the AJAX, so we can hide the inputs
when the game is over. One issue at the moment is that when the page is
first loaded, the input controls are visible even if the game is over.
AJAX fully functional

The game can now be played without ever reloading the page.