Drag/drop support for document type properties and tabs

This pull request is an implementation of drag/drop for properties and tabs - issue U4-156.  It's been reapplied using the code from the Codeplex pull request.

For properties it extends the current code using jquery ui sortable to allow dragging and dropping between tabs. 

For tabs I've hidden the existing text fields for entering the order, and applied a similar method to update their values on sorting the tabs.

Please note for this PR it's only the commit "Drag/drop UI for document type properties and tabs" you want.  Unfortunately the other commit provided in another pull request has also come in - probably as that one was done in master.  Hopefully you can separate it out OK.