#149343: When changing layouts, content would disappear if moved to a panel that already contained content.

#149375: New "add content" in the panels modal -- with categories and a bunch of new icons. Thanks *very* much yoroy!

#146169: Send the panels AJAX URL via a drupal setting to display_editor.js so that the URL will be appropriate to the Drupal installation.

New javascript drag & drop; menu_rebuild on panel page save; fix add content button positionin garland

Initial commit of Panels 2. This is *very very* alpha -- does not yet fully include an upgrade path (er well it might but I put it in and haven't tested it) and there are still obvious bugs and deficiencies.