Add a new permission to permit rebasing changes in the web UI

So far only the change owner and submitters are permitted to rebase a
change in the web UI by pushing the 'Rebase Change' button. This change
introduces a new access right that can be assigned to other users to
permit them to do the rebase in the web UI as well.

Change-Id: I21e9981bd685f1d69e792abbd7eeaf1a60d039b8
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
5 files changed