Avoid looking up standard charsets in security libraries

In many places standard charsets are looked up via their names, for example:
"Mighty Aphrodite".getBytes("UTF8")

This could be done more efficiently with use of java.nio.charset.StandardCharsets:
"Mighty Aphrodite".getBytes(UTF_8)

The later variant also makes the code cleaner, as it is known not to throw UnsupportedEncodingException in contrary to the former variant.