nb-tabset is not fully responsive

### Issue type

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

* [ ] bug report
* [x] feature request

### Issue description

The nb-tabset is not fully responsive. Even when setting the [responsive]="true" and assigning a tabIcon, the tabs are not resposive if the icons also overlap the screen. The best approach would be to have an `overflow: scroll` on the tabs. I have tried adding it, but then it scrolls my entire nb-tab and not only the tab headings.

**Current behavior:**
Tab headings are not responsive, if too many tab headings, they break the layout.

**Expected behavior:**
I would like the tab headings to be scrollable if they are too many.

**Steps to reproduce:**
Use a tabset with at least 5 icons and then view on mobile.

**Solution in the meantime**
For anyone else having this issue in the meantime, this is how I resolved it:

Override the style for the tabset like so:

```
ul.tabset {
overflow-x: auto !important;
overflow-y: hidden !important;
}
```