FEATURE REQUEST: LinkChooserPanel

[DanielSwain]

LinkChooserPanel would provide a panels-based interface to easily set the value for a field that is defined on a Django model. And, more specifically, if the field is defined as UrlField, the LinkChooserPanel should not show the Page option. On the other hand, if the field is defined as SlugField, either the Page selection option or the slug option should be allowed. Ideally, on the client side, entering a value into one field causes any other value to be blanked out.