Add one shot state transfer for multiple substates

Currently (<= 2.5) each sub state transfer requires separate state transfer invocation for each sub state. It would be very convenient if we could transfer a list of substates all in one underlying state transfer. This would require introduction of a new method in JChannel API, however we should avoid additional callbacks on application level. Proposed API for additional JChannel method is:

public boolean getState(Address target, List<String> state_ids, long timeout) throws ChannelNotConnectedException, ChannelClosedException;