Independent sub FormController via not-required attribute - #5037

<ngForm name="parent" ng-submit='saveModel(model)'>
  <button ng-disabled='parent.$valid'>Save</button>

  <!-- Colours -->
  Selected colours:
  <ul>
    <li ng-repeat="colour in model.colours">{{colour.name}}</li>
  </ul>

  <!-- colour selector subform -->
  <ngForm name="aux" not-required>
    <input type='text' ng-pattern='colour' required ng-model='newColour' />
    <button ng-disabled='aux.$valid' ng-click='addColour(colours, newColour); newColour=null'>Add</button>
  </ngForm>


  <!-- Fabrics -->
  Selected fabrics:
  <ul>
    <li ng-repeat="fabric in model.fabrics">{{fabric.name}}</li>
  </ul>

  <!-- fabric selector subform -->
  <ngForm name="aux" not-required>
    <select ng-options='opt in fabricOptions' required ng-model='newFabric'>
      <option value=''></option>
    </select>
    <button ng-disabled='aux.$valid' ng-click='addFabric(fabrics, newFabric); newFabric=null'>Add</button>
  </ngForm>
...