Casbin model syntax and semantics check on Dashboard UI

Casbin dashboard has a page for models. We want to check whether the user has written a correct Casbin model or not. If it has syntax error, we want to prompt the error line and error reason. Just like IDE showing compile errors for languages like C++ or Java.

The syntax and semantics check can be done by frontend (like codemirror) or backend (run it on a Golang casbin enforcer) or mix the above two ways.