Improve gradle scripts (exclude :modules project from Java-based ones)

modules/build.gradle

@@ -1,6 +1,25 @@
 subprojects {
+    apply plugin: 'java'
+    apply plugin: 'org.jetbrains.kotlin.jvm'
     apply plugin: 'kotlin-kapt'
 
+    repositories {
+        mavenLocal()
+        mavenCentral()
+    }
+
+    group 'io.bartek'
+    version '1.0-SNAPSHOT'
+
+    sourceCompatibility = 1.8
+
+    compileKotlin {
+        kotlinOptions.jvmTarget = "1.8"
+    }
+    compileTestKotlin {
+        kotlinOptions.jvmTarget = "1.8"
+    }
+
     dependencies {
         // compileOnly important!!! We do not want to put the api into the zip file since the main program has it already!
         compileOnly project(':api')
@@ -40,7 +59,7 @@ subprojects {
     }
 }
 
-clean {
+task clean {
     dependsOn subprojects.clean
 }
 
@@ -48,4 +67,6 @@ task assemblePlugins(type: Copy) {
     dependsOn subprojects.assemblePlugin
 }
 
-build.dependsOn assemblePlugins
+task build {
+    dependsOn assemblePlugins
+}