Improve initiation of JS and PHP-set constants

Use the $(function(){}) feature of jQuery for timing the init function,
and put defNumPlayers in an inline script as a global constant for
scorecard.js to reference in that init function.
Remove date from headers

There's no point to having it, and it's easy to forget to update it, so
it's not reliable.
Update scorecard.js header

scorecard.js isn't really a library; it's the primary javascript code.
Change PHP constant variables to constants
Fix several basic HTML and JS errors