Let project aeccessible by limited people

1. Create a group in "People" page
2. Add allowed people in the group
3. Select the project, and select "Access".
4. Add a new reference with "refs/*", and new "READ" rule.
5. Add the group inside
6. Select "exclusive" option
7. Save the change

Forbid pushing code into branch directly without code review

1. Choose "All Project" in "Project" page, and select "Access".
2. In ref/heads/* page, move to "PUSH" permission.
3. Provide "Allow" to administrator, and "Deny" to registered users and project owners.