Initial commit of content API into ctools. Only one content type is ported, but there are some docs.

Updates to smooth out problems with the new panel page type, remove deleted displays properly and other fun fixes.

Update export to make it more useful for Panels which does not always export in a straightforward manner.

Implement titles; this caused a retooling of the return value of the context task handler rendering so be sure to sync up.

#364167 by drewish: Prevent a broken UI when the number of handlers does not match up to settings on a page.

Allow plugins to have a process callback so they can modify the plugin directly to provide smarter defaults, plus add some more formal documentation in the advanced help.

Make sure base url is properly removed from task handler operations links which are not really links.

Retool the access plugins to allow multiple plugins plus and/or switch. Retool selection criteria to use this allowing for a much richer selection of task handlers on a given page.

Checkpoint checkin. Lots more interesting functionality -- pages can now be set to "single" or "multiple" task handlers, and having "single" removes the task handler arrange UI. Please some serious code re-organization so that Panels can have just one context-based task handler for multiple tasks.

Checkpoint checkin: Can now create arbitrary pages! Yay. Task handler manipulation on arbitrary pages works, though there are some clear disconnects in the UI that will be addressed next. Not all page admin functions exist yet (no clone, enable, disable, revert, delete). Not all arguments have criteria yet.

Checkpoint checkin. Partial implementation of page task with generic subtasks, plus revamp of arguments, new access plugins (stolen from Views), updates to the wizard to make it fully compatible with the modal and some minor improvements to make it more flexible.

A tool to facilitate multi-step wizards. I do not think this is quite finished yet but it handles the simple case pretty well.

- a tool for AJAX, which is the next generation tool based on what Views uses.
- a tool for modals -- completely ripping the modal out of Panels.
- moving plugins for 'arguments', 'relationships' and 'contexts' into CTools.