Once a deal is on a Submitted Invoice - Lock the deal down fully

Currently once a deal is on a submitted invoice, it puts a warning on the top of the deal and user  no longer has ability to delete the deal. 

Users are still able to change the PTR, DA and other components of the deal.  

Having a setting to lock down the deal fully once invoiced as an option for clients would be helpful feature request for some clients that want their historical deal of record locked in once invoiced.  Some other clients may not care and want to have ability to change deals even after invoiced.