* Initial implementation for git statistics in Activity tab

* Create top user by commit count endpoint

* Add UI and update src-d/go-git dependency

* Add coloring

* Fix typo

* Move git activity stats data extraction to git module

* Fix message

* Add git code stats test

* fix units permission problems

* fix some bugs and merge LoadUnits to repoAssignment

* refactor permission struct and add some copyright heads

* remove unused codes

* fix routes units check

* improve permission check

* add unit tests for permission

* fix typo

* fix tests

* fix some routes

* fix api permission check

* improve permission check

* fix some permission check

* fix tests

* fix tests

* improve some permission check

* fix some permission check

* refactor AccessLevel

* fix bug

* fix tests

* fix tests

* fix tests

* fix AccessLevel

* rename CanAccess

* fix tests

* fix comment

* fix bug

* add missing unit for test repos

* fix bug

* rename some functions

* fix routes check

* Replace all ctx.Handle with ctx.ServerError or ctx.NotFound

* Change Handle(403) to NotFound, avoid using macaron's NotFound

* Integration test for activity page

* Small code refactoring for acitvity page

* Move activity stats calculation logic to model

* Add Activity page to repository

* Add request data for activity

* Add issue data for activity

* Add user unit right checks

* Add releases to activity

* Log repository unit loading error