Allow edit of all pledge fields while pledge status is Pending

Based on feedback on the forum and discussion w/ Lobo - we should modify our pledge edit rules a bit as follows:

If pledge status = Pending (i.e. NO payments have been made on the pledge yet), all fields in the Pledge form are editable.
Under this condition, the postProcess() on Update mode will DELETE all existing pledge_payment records and then recreate them using the form values (this part is the same as when we create a new pledge).

For all other pledge statuses - existing set of editable fields is retained.

ALSO - please fix these bugs in the Selector row actions....

Expected Behavior : We should show 'Delete' action for all the pledges irrespective of their statuses and give an appropriate warning. Deleting a pledge would result in the deletion of pledge, pledge_payment records, and associated contribution records.