Alert author when moving page results in duplicate url
When creating child pages and moving them to be the same level as the parent results in duplicate url, alert the author that moving will result in a duplicate url and require the author to make a change.
Steps to recreate:
1. create a parent page titled Monday Tips (url ends with /monday.tips
2. create a child page called Monday Tips (url ends with /monday.tips/monday.tips
3. moving the child page to be a at the same level as the parent would result in a duplicate url (/monday.tips. Opti doesn't allow duplicates and appends a numeric value to the end of the moved url (/monday.tips1, but there is no alert/warning to the author that this was done and/or that this was a duplicate.
