upgrade rubocop v0 to 1 and capybara v2 to v3 🚀

Created by: adipasquale

• remove capybara-selenium, not updated since 2014 and not useful since a long time ago
• upgrade capybara from 2.15 to 3.34 . We cannot simply use ~> 3 because it points to 3.31 which has an incompatible dependency with rubocop on regexp_parser.
• upgrade rubocop from 0.8 to 1.8
• enable many new cops + autocorrection + manual corrections