Made kindlegen working on windows (including paths containing umlauts)

Added back buttons on edit mail, edit user, and edit book

cps/templates/user_edit.html

@@ -91,6 +91,9 @@
     </div>
     {% endif %}
     <button type="submit" class="btn btn-default">{{_('Submit')}}</button>
+    {% if not profile %}
+      <a href="{{ url_for('user_list') }}" class="btn btn-default">{{_('Back')}}</a>
+    {% endif %}
   </form>
 
   {% if downloads %}