Feature/fix redis leak windowmanager

The window manager didn't clean up everything when a key was expiring (not ACKed in time). 2 kind of data was pilling up:
# the list of expired message key
# the data of each message

Also one modification the general prefix keys in redis has been changed. Now each window manager has the following key: "middlewarewindows:[transport_name]:...." while before it was "middlewarewindows:[transport_name]:[transport_name]:...." .... thinking about it this might need to be changed in order to get more secure naming.