How to keep menu open while navigating to child pages.

### Issue type

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

* [ ] bug report
* [ X ] feature request

### Issue description
I am trying to navigate inside menu option and details page, it should keep it open when going inside details page..

**Current behavior:**
The menu collapses

**Expected behavior:**
the menu to be open.

**Steps to reproduce:**

```
export const DASHBOARD_ITEMS: NbMenuItem[] = [
{
title: 'Home',
icon: 'nb-home',
link: '/home/dashboard/home',
home: true,
}];

@Component({
selector: 'ngx-admin-dashboard',
template: `




`,
})

```

example if i hit route '/home/dashboard/home/info' it marks home inactive.

### Other information:

NPM 6.4.1
Node 10.15.1
os linux mint 18.3,
browser chrome.

**Angular 5, Nebular 2.00rc**