Added handling for missing flask-wtf dependency

Added CSRF protection (via flask-wtf)
Moved upload function to js file
Fixed error page in case of csrf failure

cps/templates/book_edit.html

@@ -23,6 +23,7 @@
 {%  if source_formats|length > 0 and conversion_formats|length > 0 %}
   <div class="text-center more-stuff"><h4>{{_('Convert book format:')}}</h4>
       <form class="padded-bottom" action="{{ url_for('editbook.convert_bookformat', book_id=book.id) }}" method="post" id="book_convert_frm">
+          <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
           <div class="form-group">
               <div class="text-left">
                   <label class="control-label" for="book_format_from">{{_('Convert from:')}}</label>