Adds a Gradle task that generates Javadoc for the entire project, with nice links and source references.
The stock Gradle tasks generate Javadoc strictly within the module, so (for example) any common class references in the worker are prefixed with the entire package names and links are missing. Having to keep track of three tabs of different Javadoc sites is not nice, so unification is important if we want developer-friendly documentation. And one of the important lessons of this year is that such documentation is very scarce.
Additions
A new Gradle task fullJavadoc that generates Javadoc for the entire project
Test and Review
To be filled in by the reviewers
There are no unnecessary files present in the MR
The continuous integration has no problems with the MR
The MR is filled in as requested (including labels, milestones, and reviewers)
