Update: added a "result flag" to server message template.

Added a data-result-flag attribute, that has a value of either
true or false, to the interface-message-text span in the _top.html
template. The attribute was created so that we can have something
to look for if we decide to make custom JavaScript-assisted editing
interfaces for the CMS and the TMS.

For example, we might create a site where, if the user were logged
in, there will be an extra article editing interface embedded on
the template so the user doesn't need to go to the default CMS any
more. That embedded interface will be posting the edits via an AJAX
function, which will be looking for the span interface-message-text,
which in turn has the data-result-flag, in the response page to
determine whether the edit was saved successfully.