Mouse-over cursor for nb-contextMenu is text icon, not a hand (to indicate it's clickable)

### Issue type

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

* [X] bug report
* [ ] feature request

### Issue description

**Current behavior:**
The button for a nb-contextMenu does not change the cursor to a hand icon on mouseover to indicate that the button / user profile info is clickable. Users may not know that this is clickable as a result

**Expected behavior:**
A hand icon cursor on mouseover of the element by default

**Steps to reproduce:**
Hover over the user info on the top right of the ngx-admin sample and you will get a text input cursor instead of a hand-point cursor - same for the Nebular documentation of the element