#841824 by levacjeep: Extend panels_edit and panels_edit_layout to allow more options with the $destination.

#749504 by hefox: Add a bit of documentation explaining that block.tpl.php ignores Panels specific block fields.

the renderer plugin. This backdoor shouldn't see much use in the
initial IPE release, but the general pattern is one that our javascript
will follow moving forward. Therefore, including it now.