Change default Link type in editor

[Carlos]

IMO a gsconfig setting to be able to disable the "link to local page" option would be nice anyway. This would be useful for:

- sites with many pages
- sites where most links are to external ones
- sites using the I18N plugin with a custom permalink structure having %language% or %nondefaultlanguage%, where links in the dropdown are broken - even the plugin itself could disable this.