Improve HTML generated by Scaffold

This patch improves the HTML code generated by scaffold including all elements within

. This markup is HTML Strict valid.

for example, in show.html.erb the actual scaffold generates

<%= link_to 'Back', posts_path %>

and with this patch, the result is

<p><%= link_to 'Back', posts_path %></p>

This patch affects: index.html.erb, show.html.erb, edit.html.erb and new.html.erb