Improve the renderer selection framework. This framework has no UI, but it utilizes exportables and new choices can be hand crafted.

#844062: Turned the normal drag and drop editor into a renderer plugin, made the IPE part of it. Also some fairly serious code reorganization.

Deprecated panels_get_panels() function. This will be eventually disappear. Use panels_get_regions() instead.

restored with its original functionality.

Credit for this patch goes 100% to drewish for getting me beer.

This is a major change, though one that shouldn't affect any existing
Panels implementations (unless they're using region styles in a totally
unanticipated way). Rather than having style plugins with region support
call panels_render_pane() themselves on a pane content object, this
change moves that logic further up into the render pipeline and simply
passes the regions an array of already-rendered/styled/themed pane
output.

relevant docblocks.

logic with its old wrapper (panels_render_pane()) into a single method
on the renderer for readability.

updated appropriate docblocks.

respective docblocks.

encapsulated polymorphism (display renderer). Though the core effort
should probably employ top-level polymorphism, encapsulation is fine for
the current purposes, and makes backwards compat a LOT easier.

submit callbacks.

approach was old and crusty.

Introduce the Panels stylizer module which builds on the CTools stylizer base to create user definable, recolorable styles.

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

#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).

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Remove some outdated, unnecessary files and add jQuery version protection so that multiple copies of jquery or other things do not mess us up.