Removed `gitrepo.RunCmd*` functions, because gitcmd.Command works with
Repository directly.
Move some "local filesystem" related function into "localfs.go"
1 Move `IsRepositoryModelOrDirExist` and `CheckCreateRepository` to
service layer
2 Use `gitrepo.Pushxxx` instead of `git.Push` when possible
3 use `gitrepo.Clonexxx` instead of `gitrepo.Clone` when possible