HeaderCreate silently overwrites existing license subject

[jrudolph]

It seems that projects which include code from other code bases will easily break license conditions by using sbt-header because the default behavior is to overwrite the copyright subject with whatever is defined in the build. This is obviously very bad, legally and also against the open source spirit.

The default behavior should be to never change copyright notices originating from third-parties.

[hseeberger]

I think it would be very tricky to distinguish between an outdated header and one copied over from a third-party.

Wouldn't it help to exclude such copied files with an excludeFilter?