HONEYCOMB-405 - Revert fix for indirect updates

HONEYCOMB-405 - Revert fix for indirect updates

If indirect update(delete+create) fails in a way, that delete passed,
but update part failed, delete part must be reverted

Moves reverter creation to MDTG and test cases related too it to
ModifiableDataTreeDelegatorRevertTest

Fixes tracking of allready processed changes by tracking them
from perspective of processModifications() method

Introduces UpdateFailedException as replacement
for BulkUpdateException(now thrown also for single updates)

Separates ReverterImpl from FlatWriterRegistry and ads unit tests

Change-Id: If0066d0716d9476be89b1d99985b6745becac15e
Signed-off-by: Jan Srnicek <jsrnicek@cisco.com>