Centralize build list for CSS and JS

[johnbender]

It may be that I'm the only person who forgets to add new files to tje build.xml, the Makefile, and js/index.php, but it would be good to have these lists in a single place.

[toddparker]

@johnbender - I'm closing this as an issue...we should make a wiki page for dev tasks:
https://github.com/jquery/jquery-mobile/wiki/Dev-tasks