Handle config/schema changes gracefully

[schmijos]

I removed a database column without restarting the server. Visting hotsheet/rows then raised:

ActionView::Template::Error (undefined method `editable_attributes' for class Row):
     6:   <table>
     7:     <thead>
     8:       <tr>
     9:         <% @model.editable_attributes.each do |attribute| %>
    10:           <th><%= attribute %></th>
    11:         <% end %>
    12:       </tr>

It would be cool if Hotsheet could reload its config in development.