support succinct representation of messages in messagestores

currently one-to-all messages is useful only for reducing network transfer, but at the server side, before processingRequest, the messages are broken down into bytearrayvertexidmessages, thus, each message is still stored as many times as the number of vertices it is sent to.

in this task we implements two message-stores that can represent messages in a very succinct way
especially useful when messages are of significant size & fanout is low [note that this is - useful only when no combiners are used]

this depends on GIRAPH-907 & GIRAPH-908