PySide GUI alternative for LiveMonitoring extension

The existing live plot functionality in /train_extensions/live_monitoring.py (LiveMonitor.follow_channels) uses matplotlib's interactive mode to continuously update the plot within a while loop, but the plot was not displaying at all for me (on Ubuntu 14.04). I've had trouble in the past trying to use matplotlib's interactive mode in this way, with inconsistent behavior between Ubuntu and Windows, and I think the reason is that ion() is really intended only for interactive updates directly from the terminal and may or may not happen to work in constructs like loops. For this sort of dynamically updating use case, the recommended approach seems to be using a UI toolkit (see e.g. http://stackoverflow.com/questions/1940387/interactive-mode-in-matplolib).

This proposed modification adds a basic implementation of a PySide Qt-based GUI for live-plotting the channels (as a new method, LiveMonitor.follow_channels_qt, since I assume the original method may work as intended for some people without the need for an extra dependency). This is just a basic display of the plot, but it would be straightforward to add other dynamic UI features such as the option to select and change the plotted channels while the plot is running.

I also fixed a typo in the original follow_channels method.