Demo for single and group sessions using threaded clients

[naerymdan]

Once compiled, simply run with a program argument indicating the number of clients to use. (min 2, max 26)

If there are 2 clients, it will start a single session between them using a static server for preKey fetching and exchange.

If there are more than 2 clients, a group session will be started instead.

Requires Java 1.8

[tobilarscheid]

I did not yet go through your example, but I do really like the idea of having an end to end example. +1 from me!