Custom component (or HTML) instead of menu title

### Issue type

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

* [x] bug report
* [ ] feature request

### Issue description
It is not possible to place a custom component or at least HTML tags within the menu item. Currently the interface allow only string (title) ...

I would appreciate an example code to solve this limitation, even if it contains extending nebular framework classes.

Thx, Yohay

**Current behavior:**
menu item expect title, icon, link .... but not html string or angular component. So, there is no way to place at a menu button badge or anything other than string

**Expected behavior:**
Expecting to be able to initiate menu item with:
html:

Hello

or
component:

Please advice,
Yohay