Add application plugin to allow gradle run

build.gradle

 plugins {
+	id "application"
 	id 'java-library'
 	id 'eclipse'
 	id 'maven-publish'
@@ -44,10 +45,14 @@ java {
 	withJavadocJar()
 }
 
+application {
+	mainClass = "de.tla2b.TLA2B"
+}
+
 jar {
 	manifest {
 		attributes([
-			"Main-Class": "de.tla2b.TLA2B",
+			"Main-Class": application.mainClass,
 		])
 	}
 }