Could not find search option in nbselect control (like ng2-select2).

### Missing functionality in nbselect control

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* [x ] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**
Could not find search option in nbselect control like ng2-select2 default control

**Expected behavior:**
Expected to have that option in nbselect control

**Steps to reproduce:**

**Related code:**

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