Editorialization of last merge

- change the secret/secrets code so that it will work in both old and new
  Mojolicious versions.
- Add information that perl modules can be installed from distribution
  package repositories, and not neccessarily from cpan
- Add more description to information on config file
- Revert default config to previous state
- Add tests (to be run by explain.pl test) that check for required perl
  modules