Splitting up Git administer permissions

Introduced 6 new granular permissions for Git repository administration: Create repository, Delete repository, Rename repository, Edit policies, Manage permissions, and Remove others' locks. This splits the previous monolithic 'Administer' permission to allow for more flexible delegation of authority. Existing 'Administer' permissions are automatically migrated. New repositories are granted the full set of new administrative permissions by default. Renamed several existing permissions for clarity, including 'Force push (rewrite history and delete branches)'.