improve usage message & simply code * Shorten help output for `--database` as the good option name is enough to explain. * Fix typo in help output for `--empty' * Simplyied code by removing `dest` and `metavar` for add_argument where it was not necessary because it was already the default if those parameters are not given. * Add Intevation and Magnus as rights holder and author for 2019 and 2020.