Use bootstrap grid for signup page

This allows us to have the two sections one above the other on small screens,
with the call to action text first, and then side-by-side above the sm
breakpoint with the cta on the right.

app/assets/stylesheets/common.scss

@@ -1404,18 +1404,6 @@ tr.turn:hover {
 
 /* Overrides for pages that use new layout conventions */
 
-.users-new,
-.users-create {
-  .content-body .content-inner {
-    padding: 0;
-
-    .message {
-      margin-top: 80px;
-      padding: 20px;
-    }
-  }
-}
-
 .users-new,
 .users-create,
 .users-terms,

app/assets/stylesheets/small.scss

@@ -182,19 +182,6 @@ body.small {
     top: auto;
   }
 
-  /* Rules for the sign-up page */
-
-  &.user-new,
-  &.user-create {
-    .col6 {
-      width: 100%;
-    }
-
-    .aside {
-      display: none;
-    }
-  }
-
   &.site-about #content .attr h1 {
     font-size: 28px;
   }

app/views/users/new.html.erb

@@ -8,7 +8,14 @@
   <div class='header-illustration new-user-arm'></div>
 <% end %>
 
-<%= form_for current_user, :url => { :action => "create" }, :html => { :class => "standard-form fillL col6 inner22" } do |f| %>
+<div class="row">
+  <div class='text-muted col-sm order-sm-2'>
+    <h4><%= t ".about.header" %></h4>
+    <%= t ".about.html" %>
+  </div>
+
+  <div class="col-sm">
+    <%= form_for current_user, :url => { :action => "create" }, :html => { :class => "standard-form" } do |f| %>
       <%= hidden_field_tag("referer", h(@referer)) unless @referer.nil? %>
 
       <fieldset>
@@ -75,8 +82,5 @@
 
       <%= submit_tag t(".continue"), :tabindex => 8 %>
     <% end %>
-
-<div class='aside col6 deemphasize inner22'>
-  <h4><%= t ".about.header" %></h4>
-  <%= t ".about.html" %>
+  </div>
 </div>