[Forms] Add button control

Add an mct-control for buttons, for use in toolbars.
WTD-684.

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

@@ -0,0 +1,11 @@
+<a href=""
+   class="t-btn l-btn s-btn s-icon-btn s-very-subtle"
+   ng-class="{ labeled: structure.text }"
+   ng-click="structure.click()">
+    <span class="ui-symbol icon">
+        {{structure.glyph}}
+    </span>
+    <span class="title-label" ng-if="structure.text">
+        {{structure.text}}
+    </span>
+</a>