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

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

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.