Show placeholder image if a package has no screenshots.

app/views/packages/details.slim

@@ -11,7 +11,7 @@
 
   .small-7.medium-7.columns
     p.subtitle = @package.description
-
+    - if @package.screenshots.count > 0
       - @package.screenshots.each do |screenshot|
         .row.listview
           .small-12.columns
@@ -23,7 +23,8 @@
                 href=delete_screenshot_path(@package.name, screenshot.id)
                 onclick="return confirm('Really delete the screenshot?');"
                 ] Delete screenshot
-
+    - else
+      img src='/images/dummy/no-screenshots-upload-one.svg' width='100%'
 
     // TODO: Enable comments in a later version
     // = partial '/package/comments'