Migrate the project from Gradle Kotlin DSL to Groovy DSL: update README to reference build.gradle/settings.gradle and change code blocks to Groovy. Remove build.gradle.kts. Add runServerJar and runServer tasks in build.gradle that depend on shadowJar and launch the Hytale server (uses hytaleHome paths, assets, and optional user mods). Bump plugin manifest version to 0.0.3 and set a concrete ServerVersion string. Fixed some issues.
Allow the exclusion of files in the `.vscode/` directory to be
overridden via negated patterns (gitignore patterns beginning with `!`)
by changing the pattern in `.gitignore` from `.vscode/` to `.vscode/*`
(i.e., by ignoring the files in `.vscode/` rather than the `.vscode/`
directory itself).
