Use AppWellIcon for search results

Switch to using an application icon as per design.

We need to drop the 4 pixels padding to ensure we fit 3 icons.

There was a typo where getVisibleCount should have been getVisibleResultsCount.

https://bugzilla.gnome.org/show_bug.cgi?id=610740

data/theme/gnome-shell.css

@@ -347,7 +347,6 @@ StTooltip {
 
 .dash-search-section-results {
     color: #ffffff;
-    padding-left: 4px;
 }
 
 .dash-search-section-list-results {
@@ -445,6 +444,10 @@ StTooltip {
     background-gradient-end: #181818;
 }
 
+.app-well-app.selected {
+    border: 1px solid #666666;
+}
+
 .app-well-app:hover {
     border: 1px solid #666666;
 }