Replace iharder copy/pasted impementation with Java 8 SDK Base64 implementation

[justinccdev]

The file [1] is a copy/paste of [2]. However, from Java 8, the SDK has an implementation of Base64 [3]. The iharder implementation should be replaced with SDK calls.

[1] https://github.com/MICommunity/psi-jami/blob/master/jami-core/src/main/java/psidev/psi/mi/jami/utils/checksum/Base64.java
[2] http://iharder.sourceforge.net/current/java/base64/
[3] https://docs.oracle.com/javase/8/docs/api/java/util/Base64.html