i18n support

### Issue type

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

* [ ] bug report
* [x] feature request

### Issue description

In my ngx-admin fork, I have setup translation using ngx-translate and it looks like this :

My issue is regarding nebular components, because it appears (unless I'm missing something) that the only way to add i18n support to those, is to copy them into my ngx-admin project and add translation from there.
I can help you out with this if you want, but I'm not sure what would be the best way to include it in the package in a clean way

**Current behavior:**

Nebular components are not translated.

**Expected behavior:**

There should be a way to change the language at start and on the fly.

**Steps to reproduce:**

**Related code:**

### Other information:

**npm, node, OS, Browser**

**Angular, Nebular**