Increase zIndex of the tooltip as it's now displayed inside modal

specify zIndex by using vars from modal zIndex

app/assets/stylesheets/shared/question-mark-icon.scss

@@ -56,6 +56,7 @@
   margin-left: -7.4rem;
   margin-top: -0.1rem;
   background-color: transparent;
+  z-index: $modal-zIndex + 1;
 
   .background {
     position: fixed;

app/assets/stylesheets/shared/variables/variables.scss

@@ -4,6 +4,9 @@ $white: #fff;
 $dynamic-blue: #3d8dd1;
 $teal-500: #0096ad;
 
+/* Defined in foundation-rails components/_reveal.scss */
+$modal-zIndex: 1005;
+
 @font-face {
 	font-family: 'OFN';
 	src: font-url('OFN-v2.eot');
@@ -22,4 +25,4 @@ $teal-500: #0096ad;
   font-style: normal;
   font-variant: normal;
   text-transform: none;
-}
+}