K1, Mahendra | #800 | updating lastUpdated field before upserting org units
Revert "Revert "Revert "K1, Mahendra | #800 | saving system time when org unit was last updated"""

This reverts commit 15db0352ddff7f2fa00a8af6427b79329d9f3cfe.

Added lastUpdated field to orgUnitRepo. Don't need to do it for every orgunit type.