Separating core admin behaviour from theme-specific behaviour

Changes to better support admin themes that want to do something
different from the default behaviours for tab reordering, extend drag
and drop, and field expanding.

Behaviours of the default theme considered "not core" have been moved
into a new file that resides in the theme's folder and runs immediately
after admin.js.php.
Support for themed jPlayer skins

Check for a "jplayer.css" file in the active theme's stylesheets folder.
Making Cascade module and Audio feather compatible with lazy-loaded scripts
Added support for loading linked scripts
Removed linked script loading

Don't want to be constantly loading duplicate resources into the DOM
Refactored linked script insertion

Responding to the "scripts" trigger instead of trying to insert the
same jplayer script every time the feather is loaded – this causes
duplicate resource loads when there is more than one audio feather on
the page.
Added noscript fallback

Error message and direct link to file when JS disabled.
Removed unnecessary id

Was going to use it to display the jPlayer GUI but jPlayer does this
itself on init.
Removed MSIE browser exception for sortable feathers

No comment in the code but I'm gonna take a wild guess this was
intended for IE6, in which case it's not really fair to punish users of
IE7-10.
Fix ajax Cascade module
Merge pull request #5 from onmoon/patch-6

Adding cascade module support to Firecrest's archive page
Cascade module: update page description and "next page" link

Incorporating contributions from @onmoon
Reinstate the click handler after replacing the next page link
Merge pull request #179 from xenocrat/develop

Admin refactoring, Cascade module update, Audio feather enhancements