Added hotkey support to viewerbase

Packages/viewerbase/client/components/viewer/layoutButton/layoutButton.html

@@ -0,0 +1,6 @@
+<template name="layoutButton">
+    <button id="layout" type="button" class="btn btn-sm btn-default dropdown-toggle" data-container="body" data-toggle="dropdown" aria-expanded="false" data-placement="right" title="Layout" rel="tooltip">
+        <span class="fa fa-th-large"></span>
+    </button>
+    {{  >layoutChooser }}
+</template>