Feature/mockito kotlin

[eepgwde]

The build system is much simpler. It only builds mastodon4j and none of the other projects. The test/assets are now test/resources. The src/{main,test}/java directories are now kotlin. The toolchain is up-to-date: Gradle 8.1, Kotlin 1.8.10 and JVM 17. The Test Environment has been upgraded. The most important change was in MockClient: the eq and any functions now use mockito-kotlin. Many changes to test source files to catch Exceptons. No changes to main files.

The 99 tests have passed. I personally haven't tested it against a live Mastodon server, but I'll be doing that next. I'm developing in parallel over on Sourceforge https://sourceforge.net/projects/mastodon4kt/