Update Rails and all dependencies

See merge request !12

It addresses a Rails security issue:
https://rubyonrails.org/2022/7/12/Rails-Versions-7-0-3-1-6-1-6-1-6-0-5-1-and-5-2-8-1-have-been-released

Update README.md

See merge request !10

Upgrade Ruby, Rails and other gems

See merge request !9

Round balances

See merge request !8

12.3499999 -> 12.35

Update Rails

See merge request !7

Upgrade Ruby to 3.0.1

See merge request !6

Update Ruby, Rails and dependencies

See merge request !5

It removes the ruby_dep dependency that doesn't work with Ruby 3

Address puma CVE and update bundle

See merge request !4

https://github.com/advisories/GHSA-7xx3-m584-x994

It fixes CVEs:
https://www.ruby-lang.org/en/news/2019/10/01/ruby-2-6-5-released/

* Update Rails from 5.2.3 to 6.0.0

* Run bundle exec rails app:update

* Install webpack

bundle exec rails webpacker:install

* Run migrations

* Update puma

* Add sass-rails gem

* Remove unused gems

* Forgot to add this gem

* Add webpacker config

Mainly to fix the nokogiri CVE:
https://nvd.nist.gov/vuln/detail/CVE-2019-5477