title: Multi-Category Dropdown using react-select
body: <p>I want to use react-select for a multi-category dropdown list. My use-case is to be able to select one option <strong>at max</strong> from each category. I have explained the given an example below where I want one item at max selected from each category. So we may have a selection like C1I1, C2I3, and C3I1. The project I have is using react-select v2.4.4 with react v15.6.2 and material-ui. Can anyone let me know how can I implement this functionality. Also, if this is already implemented or answered, please direct me towards it.</p>
  <ol>
  <li>Category 1</li>
  </ol>
  <ul>
  <li>C1I1</li>
  <li>C1I2</li>
  <li>C1I3</li>
  </ul>
  <ol start="2">
  <li>Category 2</li>
  </ol>
  <ul>
  <li>C2I1</li>
  <li>C2I2</li>
  <li>C2I3</li>
  <li>C2I4</li>
  </ul>
  <ol start="3">
  <li>Category 3</li>
  </ol>
  <ul>
  <li>C3I1</li>
  <li>C3I2</li>
  </ul>