[LOGTOOL-146] Add an attribute the LogMessage annotation which allows…

[jamezp]

… the generated code to set and reset the current threads context class loader during a log statement.

https://issues.redhat.com/browse/LOGTOOL-146

An example message gets generated as:

@Override
public final void noFormatWithCause(final Throwable cause) {
    final ClassLoader currentTccl = Thread.currentThread().getContextClassLoader();
    try {
        Thread.currentThread().setContextClassLoader(this.getClass().getClassLoader());
        super.log.log(FQCN, INFO, noFormatWithCause$str(), null, cause);
    } finally {
        Thread.currentThread().setContextClassLoader(currentTccl);
    }
}