nb-select: Select All, Unselect All, and type ahead search feature request

[ashwin-kambli]

Issue type

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

• [ ] bug report
• [x] feature request

Issue description

Current behavior:

Currently, the nb-select component does not support the following features:

1. Select All
2. Unselect All, and
3. Type ahead search features

Expected behavior:

It would be provide a great usability boost if the above 3 features are supported by the nb-select component.