Functional select. Custom template.

### Issue type

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

* [ ] bug report
* [x] feature request

### Issue description

**Current behavior:**
Can not use custom template for option.

**Expected behavior:**
Do we have possibility create custom template(option)?

**Steps to reproduce:**

**Like this:**

```

{{item.name}}

```

**instead of:**

```

Option empty
Option 0
Option 1
Option 2
Option 3
Option 4

```

Lacking a lot of functions as in this select https://ng-select.github.io/ng-select#/templates