Update Docx4J Version

[ingomohr]

As discussed w/ the team, we want to migrate to the latest docx4j-core version.

Apparently, this might fix a problem w/ incompatibilities of Word templates created w/ Office 2016 and which are corrupt after saving.

[ingomohr]

⚠️ We need to test carefully whether flexmark still works w/ that new API/version. (I'm adding this b/c the the API is a different Maven component - it's not just a new version.

[ingomohr]

Change

• Removed unused classpath entry for non-existing folder "src/main/resources" which caused an error marker when building in Eclipse
• Raised version to 3.0 (we're switching to another Mvn component. Cannot make sure that Dox4j API still is backwards compatible w/ the version used before)
• Replaced travis CI w/ Github Actions
• Updated all Mvn dependencies for testing and compiling
  • Replaced old docx4j dependency w/ docx4j-JAXB-ReferenceImpl 8.3.4
    • This is the latest version available for Java 8. Version 11+ requires Java 11 (which we cannot use right now)
  • Removed jaxb dependencies. They are no longer required.

No Change

• Didn't Update Flexmark b/c the latest version (2022) requires Java 11+
  • Our version we're using is still the same from 2020.
• Didn't change any code
  • All tests still pass the same as before ✅