Turn off ajax load for Selection Criteria tab in Page Manager, such that access plugins can properly load their own js files.

#683162: Convert all plugins to use new $plugin = array() format. This is less brittle than the specially named hook.

#612704 by c960657: panels_get_pane_content() inappropriately created a blank context when no contexts were available.

#657474: Fix to export logic to ensure that title_pane behavior works properly on exported panel displays.

#624710: fix an old, old bug where the default empty context was not being appropriately wrapped in an array.

#607420: Visibility rules did not appear in the list when added to a pane (though they still applied).

#606980 by Deciphered and sethfreach: Typo caused panel-pane class to disappear if another class was assigned.

Rename the original $content in panels-pane to $output so it doesnt get overwritten by the $content in the template.

Add a new field to allow setting a panel title from one of its panes.

Remove some outdated, unnecessary files and add jQuery version protection so that multiple copies of jquery or other things do not mess us up.

#568218: Links to clone, export, delete/revert, enable/disable variants from the main summary page were incorrect and led to an operation trail not found message.