Use the combined ArgparseConfigParser from openmicroscopy/yaclifw#5

See openmicroscopy/yaclifw#5
* I've completely removed the parsing of environment variables (`EnvDefault`)
* Default branch changed from `OMERO-trunk` to `OMERO-5.0-latest` (`omego` defaults to `ICE=3.5` if a label isn't given)

TODO: Example config files