Use $Opt["strictJavascript"] to add "use strict"; to script.js.

Safer than enabling it globally, although eventually I will do that.
At the same time make the inclusion of .css files safer: only allow
cacheable.php to return whitelisted CSS files.

Also a little JS fix.
Consistently call them paper ADMINISTRATORS.
Internal: Refactor a bit of JS.
Rename meeting navigator to meeting tracker, a better name.
Document meeting tracker.