WIP: update .js, .css, routes.rb, and task via rake task
customer_cards.rake: use better needle to insert after existing mounted engines
custom_cards.rake: no need to register tasks anymore
custom_cards.rake: better needles for application.{js,css}.erb
Merge pull request #559 from Tahi-project/gem-simplication

[#79989900] simplify custom .gem installation