BUG Fixes #133. Disable click on SubmittedObject's GridField rows.

WorkflowInstances may not belong to users when passed to an
AssignUsersToWorkflowAction. Therefore we prevent CMS errors when
table rows & edit icons are clicked in "SubmittedObjects" GridField.

- Additionally, we visually indicate these records as 'disabled'.
- Also fixes AJAX 404 before redirection when clicking hyperlink.
Merge pull request #140 from phptek/issue/133

BUG Fixes #133. Disable click on SubmittedObject's GridField rows.