Add IPE permissions for changing pane settings or deleting panes

Trying out the new IPE for the first time on a project - it's amazing :)

I was thinking it may be useful to add permissions for the 'pane settings' and the 'pane delete' button as well - I can imagine use cases where you only want to expose the 'move pane' functionality, or the style button.

Attached patch adds two new permissions and adds checks for those in panels_ipe.module.