Migrated core and extension modules to Kotlin

(Except BitmessageContext and Bytes)

core/build.gradle

@@ -28,6 +28,6 @@ dependencies {
     compile 'ch.dissem.msgpack:msgpack:1.0.0'
     testCompile 'junit:junit:4.12'
     testCompile 'org.hamcrest:hamcrest-library:1.3'
-    testCompile 'org.mockito:mockito-core:2.7.21'
+    testCompile 'com.nhaarman:mockito-kotlin:1.4.0'
     testCompile project(':cryptography-bc')
 }