Use separate library to do base64 encoding in Java

default and jersey2 clients to make it work in both JVM and Android

modules/swagger-codegen/src/main/resources/Java/libraries/jersey2/pom.mustache

@@ -152,6 +152,13 @@
       <version>${jodatime-version}</version>
     </dependency>
 
+    <!-- Base64 encoding that works in both JVM and Android -->
+    <dependency>
+      <groupId>com.brsanthu</groupId>
+      <artifactId>migbase64</artifactId>
+      <version>2.2</version>
+    </dependency>
+
     <!-- test dependencies -->
     <dependency>
       <groupId>junit</groupId>