chore: Update license headers

[christophd]

• Remove copyright year from license headers
• Update license headers
• Add missing license headers
• Use the same license header in all files

[bbortt]

damn. did you use some script(s) or tool(s) for this?

[christophd]

damn. did you use some script(s) or tool(s) for this?

IntelliJ has a copyright section where you can create a template and update the whole project. Works pretty smooth 😎

[bbortt]

cool, didn't know that!