BUG-509: Move ModificationApplyOperation

This patch moves ModificationApplyOperation at al. to the data tree
package, improving its isolation.

Change-Id: I37081222e30c149a87baf6f4a5d3ce2e84f13acb
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-509: Move ModificationApplyOperation"