Change the place where the MediaStream were creating in JingleSession.
They are now created in the contructor (and not in the method handling
the session-initiate), to that the HammerStats (the class that will take
care of the stats) can register their MediaStreamStats easily and cleanly.

To achieve that, some method of HammerUtils and JingleSession were modified.
Add an "-help" option to the program to print how to use the program
(what field are necessary).

Also add a script for linux/freebsd/mac system to run the program
(work on linux, couldn't test on other system for now).

Update the build.xml to add an jvmarg to set the logging configuration file
(and add the config file in lib/)
-> now to change the logging level, change it in logging.properties