[Forms] Add CompositeController

Add a controller for composite controls; this is used
to flag contained controls as required when they have
been partially filled in (to treat entering one of two
such fields as invalid.) WTD-593.

platform/forms/res/templates/controls/composite.html

@@ -1,13 +1,15 @@
-<ng-form name="mctFormItem" ng-repeat="item in structure.items">
-    <mct-control key="item.control"
-                 ng-model="ngModel[field]"
-                 ng-required="ngRequired"
-                 ng-pattern="ngPattern"
-                 options="item.options"
-                 structure="row"
-                 field="$index">
-    </mct-control>
-    <span class="composite-control-label">
-        {{item.name}}
-    </span>
-</ng-form>
+<span ng-controller="CompositeController as compositeCtrl">
+    <ng-form name="mctFormItem" ng-repeat="item in structure.items">
+        <mct-control key="item.control"
+                     ng-model="ngModel[field]"
+                     ng-required="ngRequired || compositeCtrl.isNonEmpty(ngModel[field])"
+                     ng-pattern="ngPattern"
+                     options="item.options"
+                     structure="row"
+                     field="$index">
+        </mct-control>
+        <span class="composite-control-label">
+            {{item.name}}
+        </span>
+    </ng-form>
+</span>