perf: RBAC role building and Enforcer optimizations (#178)

* perf: rbac build role link only add some role

perf: Enforcer hold a scope pointer rather than initalize scope when enforce.

Signed-off-by: stonex <[email protected]>

* chore: move bindings to pycasbin and remove this directory.

Signed-off-by: stonex <[email protected]>

* perf: clean Enforcer scope by model config.

Signed-off-by: stonex <[email protected]>

Author: sheny1xuan