Nb Stepper Long Names Overlapping on Horizontal Alignment

### Issue type

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

* [ x] bug report
* [ ] feature request

### Issue description

**Current behavior:**
When defining multiple steps horizontally with long names and resize a bit the width of the window, the texts will overlap looking strange

**Expected behavior:**
Steps should truncate their texts with "..." when screen size doesn't allow displaying entire description for each step.

**Steps to reproduce:**
Create empty app and use NbStepper to display 5 steps with long names displayed horizontal and then resize the window.

**Related code:**

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### Other information:

**npm, node, OS, Browser**
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**Angular, Nebular**
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