Updates to send and check SMS pages

Adds a back button instead of a back link (more prominent, you’re likely to
go back on these pages if you’ve made a mistake)

Tweaks to wording

app/assets/stylesheets/components/banner.scss

@@ -10,6 +10,7 @@
   margin: $gutter-half 0 $gutter 0;
   text-align: left;
   position: relative;
+  clear: both;
 
 }
 

app/assets/stylesheets/components/page-footer.scss

@@ -3,8 +3,10 @@
   margin-bottom: 50px;
 
   &-back-link {
-    display: block;
-    margin-top: $gutter;
+    @include button($grey-1);
+    display: inline-block;
+    padding: 0.52632em 0.78947em 0.26316em 0.78947em;
+    margin-left: 10px;
   }
 
   &-delete-link {