Ark
* 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