Minor improvements and fixes

I copied the Base64 encoder from Android platform (and converted it to Kotlin) because the Java one exists only since 1.8
(I don't now if I want to curse Java for not supporting Base64 out of the box earlier, or Android for not supporting a recent Java API)

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.1.3'
+    ext.kotlin_version = '1.1.3-2'
     repositories {
         mavenCentral()
     }