Use signals to propagate commands instead of parsing logfile over and over again

[Markus Korn]

Currently lernid is creating a logfile called "classroom_temp.txt", its only purpose seems to be to pipe commands like [STARTSESSION] to the other widgets. This file is monitored for changes and parsed over-and-over again, which overall is an expensive operation.
It should be easy to add a "command" signal to IrcBackend.Room which notifies connected widgets about commands in the classroom-chat session

[Michael Budde (mbudde)]

Fix in lp:~mbudde/lernid/mbudde rev. 76