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/login.html

@@ -4,6 +4,7 @@
   <h2 style="margin-top: 0">{{_('Login')}}</h2>
   <form method="POST" role="form">
     <input type="hidden" name="next" value="{{next_url}}">
+    <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
     <div class="form-group">
       <label for="username">{{_('Username')}}</label>
       <input type="text" class="form-control" id="username" name="username" placeholder="{{_('Username')}}">