lp1836808 add cancel button to merge edit

lp1836808 add cancel button to merge edit

In the merge UI add a button so one can cancel out of editing mode

To test
-------
[1] Apply the patch and create/find a record bucket that has at least
    two records.
[2] In the Record Buckets interface, select two records and invoke
    the Merge Selected Records action.
[3] Select one record as the lead record, then click the Edit button.
[4] Verify that a "Cancel Edit" button is displayed. Make changes to
    the record, then click "Cancel Edit".
[5] Verify that the contents of the record have not changed.
[6] Click the Edit button again; verify that the record is at its
    original state. Make changes, then save them.
[7] Verify that the lead record has been updated.

Signed-off-by: Mike Risher <mrisher@catalyte.io>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>