fix(popover): prevent wrong positioning from title

If the title is blank, ngAnimate attempts to animate ngShow so positionTooltip
gets called when the title box is still visible, about to be animated to
hidden. Hence, the positionTooltip receives a taller height. Avoid this by
using ngIf instead.

Closes #3518

Author: chrisirhc

template/popover/popover-template.html

@@ -5,7 +5,7 @@
   <div class="arrow"></div>
 
   <div class="popover-inner">
-      <h3 class="popover-title" ng-bind="title" ng-show="title"></h3>
+      <h3 class="popover-title" ng-bind="title" ng-if="title"></h3>
       <div class="popover-content"
         tooltip-template-transclude="content"
         tooltip-template-transclude-scope="originScope()"></div>

template/popover/popover.html

@@ -5,7 +5,7 @@
   <div class="arrow"></div>
 
   <div class="popover-inner">
-      <h3 class="popover-title" ng-bind="title" ng-show="title"></h3>
+      <h3 class="popover-title" ng-bind="title" ng-if="title"></h3>
       <div class="popover-content" ng-bind="content"></div>
   </div>
 </div>