A WIP experiment to create a simple power select alternative. I tried to use the same argument names to make transitioning easier.

This is what the usage looks like at the moment:

    <AuSelect
      @placeholder="Kies een provincie"
      @options={{this.provinces}}
      @selected={{this.selectedProvince}}
      @onChange={{fn (mut this.selectedProvince)}} 
      id="au-select-province"
      as |province|
    >
      {{province.label}}
    </AuSelect>

Remaining things:

• styling 🙈
• Option grouping
• multi-select support? Apparently this isn't a UX-friendly or accessible option.
• @allowClear argument
• tests
• probably other things, it's a quick draft at the moment.

Closes #143