Fix stories list in index page

[Sandro-Meireles]

When creating a new story in manage/story/ it should appear on the home page, as the first item on the list, however, this does not happen. On the home page, stories are being listed incorrectly, starting from the second item.

• The problem is:
  
  

To solve this problem I changed the filter responsible for listing them.

• in templates/public_base.haml line 537

-        - for story in main_stories|slice:"1:4"
+        - for story in main_stories|slice:"0:3"

[norkans7]

That is intentional as the first story is shown on the home page on https://github.com/rapidpro/ureport/blob/master/templates/public/index.haml#L133

Just make sure you are running the latest changes a recent fix was added in #658