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

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

Attempt to be more obnoxious about letting the administrator know that Panels is out of date when it is updated without CTools.

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

calling it 'default' was misleading since sometimes the legacy renderer
actually acts as the true 'default' (the renderer that's used when no
other one is specified).

constructor by checking Panels' legacy rendering mode state.

style plugins.

renderer to determine what type of data it should be passing to style
plugins.

parameter, as that's more inheritance/interface friendly.

default is at least as accurate, but is more common and doesn't have
some of the additional meanings 'standard' does.

to the render method. I swear I've added this at least twice before, and
it keeps disappearing...

files.

it possible to pass a renderer in to panels_render_display().

renderer class, as it should (and as the docblock indicates)

panels_display object.

relying on it.