No Refresh Token expiry technique

### Issue type

**I'm submitting a ...** (check one with "x")

* [ ] bug report
* [ x ] feature request

### Issue description

**Current behavior:**

When using both access and refresh tokens, there is a tactic to refresh the access token, but not to handle when a Refresh tokens expires. My server could send a request with something like {status: 401, message: "Token expired"}

**Expected behavior:**

N/A

**Steps to reproduce:**

N/A

**Related code:**

### Other information:

**npm, node, OS, Browser**
```
OS: Windows 10
npm: 6.4.1
```

**Angular, Nebular**
```
Angular: 7.2.2
Nebular: 3.1.0
```