GetFeature and WMTS

It seems that we have lost the ability to do WFS/WMS requests on WMTS which are included in the layertree.

WMTS layers can be queryable when defined as background layers (mapopacity slider) without any problem.

But if one defines a WMTS in the admin UI and adds a WMS layer as option, nothing happens when trying to do a request, because the ```LAYERS``` parameter in empty.

Hereunder an snapshot of my layer's config. You can test that on http://sitn.ne.ch/sitn_dev/wsgi/theme/cadastre?map_x=553100&map_y=199200&map_zoom=8.

Just make a stupid click into the map... (the ```parcelles``` layer was already in use and successfully returned a response for a former WMTS background layer)

Did I miss something, or is that a bug???

![snap](https://f.cloud.github.com/assets/1681332/390910/5980b912-a751-11e2-8ebb-79ed4e1f3276.png)