How can we decode jwt token and set those value in local storage

### Issue type

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

* [ ] bug report
* [x] feature request

### Issue description

**Current behavior:**

When I get a jwt token from my API, it is automatically set in local storage under key **auth_app_token**

**Expected behavior:**

My query is- How can we decode the token we get and store those internal values inside the **auth_app_token**?

**Steps to reproduce:**

Steps to reproduce are basic steps for authentication with token class **NbAuthJWTToken**

**Related code:**

When I get the token, what I want to do is-
```
token.decode(token.getValue()) // this will give me what token consists of
{
"sub": "1234567890",
"name": "John Doe",
"iat": 1516239022,
"role": "superuser"
}
```
and this I can set to local storage.

Also while clearing I want to clear this data.
### Other information:

**npm, node, OS, Browser**
```

```

**Angular, Nebular**
```
Angular: 9.0.4
Nebular: 5.0.0

```