runeliteplus: adds preliminary Gradle support

protocol-api/build.gradle

@@ -0,0 +1,9 @@
+
+description = 'Protocol API'
+dependencies {
+  compile project(':runelite-api')
+    compile group: 'org.slf4j', name: 'slf4j-api', version:'1.7.25'
+    compile group: 'com.google.guava', name: 'guava', version:'28.0-jre'
+    testCompile group: 'junit', name: 'junit', version:'4.12'
+    compileOnly group: 'org.projectlombok', name: 'lombok', version:'1.18.8'
+}