1. Set `gon.current_project_id` in a protected branches controller,
   since that's the only place this is used.

2. Move flash notice to the redirect message.

3. Rename the `js_access_levels` method to `access_levels_options`

4. Scope a `find` while sending a branch protection email.

5. Use scopes to simplify finding users with push/merge access for a
   project.

6. Use `change_column_null`  to avoid an `ActiveRecord::IrreversibleMigration`