Switch to Groovy DSL; add runServer task

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.

build.gradle

@@ -121,6 +121,33 @@ if (hasHytaleHome) {
         return programParameters
     }
 
+    def serverJar = file("$hytaleHome/install/$patchline/package/game/latest/Server/HytaleServer.jar")
+    def assetsZip = file("$hytaleHome/install/$patchline/package/game/latest/Assets.zip")
+    def shadowJarTask = tasks.named('shadowJar')
+
+    tasks.register('runServerJar', JavaExec) {
+        dependsOn shadowJarTask
+        mainClass = 'com.hypixel.hytale.Main'
+        classpath = files(serverJar)
+        workingDir = serverRunDir.absolutePath
+        doFirst {
+            def modPaths = [shadowJarTask.get().archiveFile.get().asFile.absolutePath]
+            if (load_user_mods.toBoolean()) {
+                modPaths << "${hytaleHome}/UserData/Mods"
+            }
+            setArgs([
+                    '--allow-op',
+                    '--disable-sentry',
+                    "--assets=${assetsZip}",
+                    "--mods=${modPaths.join(',')}"
+            ])
+        }
+    }
+
+    tasks.register('runServer') {
+        dependsOn 'runServerJar'
+    }
+
     // Creates a run configuration in IDEA that will run the Hytale server with
     // your plugin and the default assets.
     idea.project.settings.runConfigurations {