Implement 'Restore Change' feature.

Now it is possible to restore status of abandoned changes to 'NEW'.
It helps in a situation when a change has been abandoned accidently.

Bug: issue 312
Change-Id: Iba61dcf82a9b5ee5b78cd529b041f92a042a9611
[cherry-picked from 32002457744e9e0c17b258fcfea5dd6d30732950]
Change-Id: Icc6dddb63689250c869189639af0d72ed8837336
15 files changed