Allow the context object to be altered by form submitters and validators

When working on combining Panelizer + FAPE I ran into an issue with the panels edit renderer which prevented content from properly being displayed after the panelizer form was complete. In my specific case I was including field edit forms on the panelizer configuration pages, allowing users to alter the values of form fields while also adjusting display properties. The core of the problem is that the panels_renderer_editor's cache property is stored within $form_state, but never gets reloaded into the renderer on submit. The following patch inspects $form_state and overwrites the renderer's context value with the one in $form_state, if present. This allows content to properly be AJAX'd in after completing the Panelizer wizard.

And yes, the description of this problem is far longer than the actual patch :)