Validator for DS configuration

[DenisKnoepfle]

To verify the whole DS configuration including spotter.conf, mEnv.xml and hierarchy.xml which will be sent to the server as a container object (see #118) a validator is required that checks the configuration and signals any errors or approves it.

The validator needs to be accessible through a new service operation which will be called by the UI periodically (every 1-2 seconds). Only valid configurations will be passed to the start operation of the diagnosis run.