Rails 5.2, Ruby 2.6.5, Rspec tests, Improved modals, Security

This release improves the modal windows for data entry, with browser-based validations and working error messages! Modern versions of Ruby and Rails are incorporated. A few tests have been included using Spec so that basic functionality can be checked automatically. As well as the security benefits of updating to recent versions of Rails and Ruby, various gems have been updated in line with security announcements concerning them.