Multiple Mapbender applications.

Instead of having one massive mapbender.yml you can now add multiple
YAML files in the app/config/applications directory. Each YAML in
there must have a top-level "parameters" key and therefore can
list any parameter desired, but especially the "applications"
parameter. The MapbenderCoreExtension takes care of loading, merging
and setting the final parameters in the container.

Right now these files are not monitored by the cache invalidation
in the dev mode, so clear the cache manually or touch the config.yml