Allow restricting contexts via access control to allow the add content UI to remove irrelevant content.

Make access plugins a little less focused on the term "access" and change selection criteria to selection rules.

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

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.