Move description inside config

With Application Templates, there was a "description" in the configuration JSON that described the resulting application. That seems to have gotten lost; the new AbstractApplication has a description, but in the case of ETLBatchApplication and ETLRealtimeApplication, these descriptions are hard-coded (and incorrect, as they refer to "Templates").

It would be better if the config files included a description field, and if that was not empty, use it instead of the hard-coded values. The default values should in any case be corrected.