fix(datepicker): fix popup element garbage collection

- Ensures the correct element is selected due to ng-if replacing element with comment tag

Closes #5274
Fixes #5058

Author: deeg

template/datepicker/popup.html

@@ -1,10 +1,12 @@
-<ul class="uib-datepicker-popup dropdown-menu" dropdown-nested ng-if="isOpen" ng-style="{top: position.top+'px', left: position.left+'px'}" ng-keydown="keydown($event)" ng-click="$event.stopPropagation()">
-	<li ng-transclude></li>
-	<li ng-if="showButtonBar" class="uib-button-bar">
-		<span class="btn-group pull-left">
-			<button type="button" class="btn btn-sm btn-info uib-datepicker-current" ng-click="select('today')" ng-disabled="isDisabled('today')">{{ getText('current') }}</button>
-			<button type="button" class="btn btn-sm btn-danger uib-clear" ng-click="select(null)">{{ getText('clear') }}</button>
-		</span>
-		<button type="button" class="btn btn-sm btn-success pull-right uib-close" ng-click="close()">{{ getText('close') }}</button>
-	</li>
-</ul>
+<div>
+  <ul class="uib-datepicker-popup dropdown-menu" dropdown-nested ng-if="isOpen" ng-style="{top: position.top+'px', left: position.left+'px'}" ng-keydown="keydown($event)" ng-click="$event.stopPropagation()">
+    <li ng-transclude></li>
+    <li ng-if="showButtonBar" class="uib-button-bar">
+    <span class="btn-group pull-left">
+      <button type="button" class="btn btn-sm btn-info uib-datepicker-current" ng-click="select('today')" ng-disabled="isDisabled('today')">{{ getText('current') }}</button>
+      <button type="button" class="btn btn-sm btn-danger uib-clear" ng-click="select(null)">{{ getText('clear') }}</button>
+    </span>
+      <button type="button" class="btn btn-sm btn-success pull-right uib-close" ng-click="close()">{{ getText('close') }}</button>
+    </li>
+  </ul>
+</div>