fixed various comm errors, added help

ServerHandler.py
+Added a check function in case the requested username has already been
taken.
-Removed commented out code

Client.py
+Added functionality to handle if the server unexpectedly disconnects
from the client
+Added a help function in case users forget commands
+Added command processing so incorrect commands don't get broadcasted to
the entire network as messages
~made the while loop controls global so that when one loop stops, so
does the other (i.e. client will never run the outgoing thread without
the incoming thread)