Rework how baseline-compare/replace work

[laeubi]

baseline-compare/replace is quite convoluted with p2-meta-data and actually "breaks" maven semantics as we possibly replace an already published artifact with new versions, what might no longer be possible in Maven 4 sooner or later.

Instead we should rework the process to the following pattern:

1. If version is known and baseline-replace is active, it searches for an existing artifact (excluding qualifier) and set all artifacts of the build to that version.
2. In this case the "package-mojos" would write the results as usual but not attach then to the project at all and instead write a properties file mentioning them as we already do for p2 artifacts.
3. baseline-compare can now compare and possibly fail / warn / ignore

That way it is also much more flexible to use these mojos in a stand-alone fashion (e.g. via CLI invocations).