Script editor support

New script editor support for plugins, plugin engine will try to use registered script editor, if none found it falls back to a generic textbox.  The codebase still needs some more cleanup, I think, but it's getting there. :smiley: 

Oh, one other thing: Using the FastScripter plugin as an embedded editor is bugged, but I can't figure out what's wrong. It screws up when entering text and doesn't appear to remember the contents when clicking OK. I can't figure out what's wrong, though, as the stock script plugin appears to work fine.