1. Introduce `Evaluator` interface which do the permission checking.
2. `admin`, `lazy`, `rbac`, `namespace` and `evaluartor` set are implemented the
`Evaluator` interface.
3. Move project rbac implemention from `project` to `rbac` pkg to reduce
the name conflict with project instance of model.
4. Do permission checking in security context by `Evaluator`.
5. Cache the regexp in rbac evaluator for casbin.
6. Cache evaluator in namespace evaluator to improve performance.
Signed-off-by: He Weiwei <hweiwei@vmware.com>
