Maven migration

[GuusLieben]

Migrate the Selene project to Maven to make it more 'enterprise ready' (aka allow us to use some specific plugins, mostly in regards to AspectJ)

Features to mirror:

• [x] Multi module project setup
• [x] Dependency shading
  • [x] Relocation of Jackson and Apache Commons
  • [x] Exclusion of expected externals
• [x] Kotlin/Java project roots
• [x] Distributed build targeting
• [x] Date/hash based build versioning
• [x] Aggregated JavaDocs / Dokka documentation (changed, see comment)
• [x] JUnit Jupiter / Mockito test environment
• [x] Automatic disposal of targets (skipped)

[GuusLieben]

Aggregated Dokka documentation is currently not possible for Maven multi-module projects. While this means there will be no JavaDocs for Kotlin types, the goal is still to add aggregated documentation for Java types.