Update mapproxy config file

[geraldo]

In case of using Mapproxy tile cache, sources, caches and layers have to be configured in mapproxy.yaml. Right now this is done manually each time a layer or group is added or renamed. In order to automatize this, the following tasks have to be implemented:

• split up different projects in separate yaml configuration files
• move actual mapproxy.yaml to mapproxy.yaml.bck
• write new yaml file, or only the parts which are defined in the actual project