Split out prerequisite validation from creation. Distinguish system prereqs from application prereqs. Support URL autodetection to eliminate requirement to edit file as part of setup.
Reviewed-on: https://gitea.subcultureofone.org/greg/tkr/pulls/58
Co-authored-by: Greg Sarjeant <greg@subcultureofone.org>
Co-committed-by: Greg Sarjeant <greg@subcultureofone.org>
