DetailsList: adding an optional column re-ordering feature

[laxmikankanala]

Pull request checklist

• Addresses an existing issue: Fixes #0000
• Include a change request file using $ npm run change

Description of changes

Column Reorder support in DetailsList using drag and drop
Based on the mouse position of the event, column target position will be decided.
There is an optional parameter to specify frozen columns to keep the position of those columns intact.

Pending things:

1. Need to test this with all different options/types of DetailsList
2. Need to fix the hit area for drag, that is being impacted by marquee selection
3. Add CSS changes to show the drag items and drop hints

Focus areas to test

Functionality of Column reorder