Fix some more instances of "Created at"

"Created on" should be used when the timestamp is only a date.

app/views/admin/groups/show.html.haml

@@ -25,7 +25,7 @@
             = @group.description
 
         %li
-          %span.light Created at:
+          %span.light Created on:
           %strong
             = @group.created_at.stamp("March 1, 1999")
 

app/views/profiles/keys/show.html.haml

@@ -8,7 +8,7 @@
           %span.light Title:
           %strong= @key.title
         %li
-          %span.light Created at:
+          %span.light Created on:
           %strong= @key.created_at.stamp("Aug 21, 2011")
 
   .span8

app/views/projects/merge_requests/show/_mr_box.html.haml

@@ -13,7 +13,7 @@
   .ui-box-body
     %div
       %cite.cgray
-        Created at #{@merge_request.created_at.stamp("Aug 21, 2011")} by #{link_to_member(@project, @merge_request.author)}
+        Created on #{@merge_request.created_at.stamp("Aug 21, 2011")} by #{link_to_member(@project, @merge_request.author)}
         - if @merge_request.assignee
           \, currently assigned to #{link_to_member(@project, @merge_request.assignee)}
       - if @merge_request.milestone

app/views/projects/show.html.haml

@@ -59,7 +59,7 @@
     %br
     .light-well
       %p
-        %span.light Created at
+        %span.light Created on
         #{@project.created_at.stamp('Aug 22, 2013')}
       %p
         %span.light Owned by