Introducing scalafix

[sebastian-peter]

Resolves #661

In this PR also

• scapegoat is removed, as it won't be compatible with Scala 3
• eol settings are set with .gitattributes. Recommended setting for git config core.autocrlf is input
• some more checks than just import order are enabled with scalafix, such as disallowing while loops or redundant syntax
• the changes made via scalafix are also enforced via CI