Move login failure text to i18n

[scottrobertson]

This text should be stored in either i18n, or in Tokenable::Config.

https://github.com/tokenable/tokenable-ruby/blob/main/lib/tokenable/controllers/tokens_controller.rb#L8

[scottrobertson]

Should be added to installer too, similar to how Devise does it:

https://github.com/heartcombo/devise/blob/45b831c4ea5a35914037bd27fe88b76d7b3683a4/lib/generators/devise/install_generator.rb#L33-L35