Data Model UI Improvements

Following improvements are suggested to make data model UI more user friendly:

1. Generate a warning, if the user accidentally leave the pane after making some changes - creating a data model involves significant data entry, all of which can be lost by a simple mistake of clicking on side pane or top-bar.

2. Allow Attribute names to be edited - attributes play an important role in system and downstream matching can be adversely affected, if the names don't match. Therefore allow attribute names to be edited in add/edit mode.