Dependeny scope of plugins is now editable

Plugin authors should now be able to edit the dependency scope on the plugin page. I hope that I adhered to the conventions, please let me know if I should change anything.

See [the thread on the mailing list](http://grails.1312388.n4.nabble.com/Publish-rights-for-Twitter-Bootstrap-plugin-td4651249.html) for more information.