handle default service type w/o pathinfo

[mkofahl]

By now, proof of concept only. This feature will allow a service type to be set as default. If no service type is given in the request, mapcache will fall back using this one. URL in capabilites is adjusted for wmts only. So please dont merge at this stage. I will complete for other service types if you find it worth merging.

Configuration:

<mapcache>
   <service type="wmts" enabled="true" default="true"/>

   <metadata>
      <url>http://example.com/mywmts</url>
   </metadata>
</mapcache>
´´´

[ruester]

I've added a new solution based on @mkofahl 's commit.
Now all service types support this feature.
Additonally the behaviour of the wms service is now working as described in the documentation (see here) if you set default="true" in the wms service type.