app/views/shared/_footer.html.erb
<%# BEWARE: this link cannot go *inside* any sort of container which reconfigures jQuery, because it needs jQuery in order to work! %>
<center>
<% if account_signed_in? %>
<%= link_to 'Sign out', destroy_account_session_path, { method: :delete, data: { disable_with: 'signing out...' }, class: 'btn', id: 'signout' } %>
<% end %>
</center>