Added Document Security to all Sales modules, Purchase modules and Campaign.  System Admin and the owner of the document can lock/unlock a document to prevent the document been edited accidentally by other user.

GUIDE

1. For System Admin, open any document.  For normal user, open any document created by you.
   
2. Click on "Activity & Security" tab.
   
   
3. If the document is not locked, anyone who can access to this dccument can make amendmend.  To avoid this, click on button "Lock Now".
   
4. Once a document is locked, an orange lock  will be shown beside the document. The document is not editable now.
5. Only the owner and System Admin can unlock a document. To do so, in "Activity & Security" tab, click on button "Unlock Now".