JAR Relocator

Fork of lucko's jar-relocator used by my plugins that require external/additional libraries to work. There are just two differences with the original version: it should avoid loading libraries' classes that do not work with the current Java version (see Java 9's multi-release JAR files) by simply ignoring them and, obviously, the package name is changed so that the JAR gets loaded even if the original version's classpath is loaded already.