ReorderContentWidget to sort content via drag and drop / little adaption to ContentContainerController

Reorder by drag and drop:
- ReorderContentWidget is a configurable javascript widget that uses jquery-ui sortable and ajax requests to send a reorder request to the server
- ReorderContentBehavior contains the logic to process such a request and reorder the elements in the database. The method used for that is also configurable for specific needs.
Adaption to ContentContainerController:
- small change. The controller now also accepts sguid/uguid as param in a POST request.