[MapProxy] add a wmts layer

[Martijn Coenen]

Raffaello:
> I'm not be able to use a wmts layer with mapproxy. Think it's buggy.
> First of all you need the MapProxy 1.5a version, you can get it from github.
>
> And the wmts Protocol implementation in mapproxy still not work (for my experience). 
> I have no tile visualization neither in OpenLayers nor Flexvierwer..

I did have something from my WMTS service via Mapproxy, but utterly unusable because the projection isn't working as it should be.
The tiles load and are stored in the Mapproxy cache, so that part is functioning as it should be.

> My conclusion is: Mapproxy have a bug on WMTS protocol implementation. GeoWebCache too.

I'd say it's a bit far to say it's a bug, more a lack of documentation and working examples about this subject ;)
I have only one layer that is giving me problems with WMTS on 1.4x, a Dutch governmental layer source that gives me trouble, but other layers are working fine (or at least as far as I tested them). So I can't say Mapproxy isn't able to do the WMTS-thing, it's just.... a bit more difficult to get it working compared to WMS :)

Regards,
Martijn