Format dashboard total downloads count

Use the format-num helper to properly comma-seperate the "Total Downloads" count
on the Dashboard page.

Fixes #855

Author: DorianListens

app/templates/dashboard.hbs

@@ -6,7 +6,7 @@
     <div id="stats">
         <div class='downloads'>
             <img class="download" src="/assets/download.svg" />
-            <span class='num'>{{visibleStats.total_downloads}}</span>
+            <span class='num'>{{format-num visibleStats.total_downloads}}</span>
             <span class='desc small'>Total Downloads</span>
         </div>
     </div>