Move to rails 6

[hellcp]

Draft PR for figuring out what's wrong and what has to be fixed still, this far:

• We abandon capybara-webkit for capybara-selenium
• espinita is installed from git, because there has not been a release in 5 years and we need the code for rails 5.1 support
• move from axlsx_rails to caxlsx_rails
• force_ssl was moved to be a part of global config instead of enforcing it in controllers
• Removed duplicate keys in config/locales/country_select.en.rb

[coveralls]

Coverage decreased (-42.3%) to 44.083% when pulling c124bb5 on hellcp:rails6 into 339d539 on openSUSE:master.

[hellcp]

FTR: the current rspec issue seems to be related to pages being empty for capybara