Add RSA key gen Gradle task

Fixes #325

util/build.gradle

@@ -1 +1,11 @@
 description = 'Apollo Utilities'
+
+task(genRsa, dependsOn: classes, type: JavaExec) {
+    def utilSubproject = project(':util')
+    def utilClasspath = utilSubproject.sourceSets.main.runtimeClasspath
+
+    main = 'org.apollo.util.tools.RsaKeyGenerator'
+    classpath = utilClasspath
+    jvmArgs = ['-Xmx1024M']
+    workingDir = project.rootDir
+}