Allow user to zoom the StateEvaluationTree using Control+Mousewheel.

This really just changes the size of the font, but everything in the StateEvaluationTree is based on the font size. The new value isn't yet stored in the user's preferences.
Scale pen width according to font size.
Add a preferences menu.

Currently allows the user to select their preferred locale for use in the TraceViewer (defaults to the system's locale). This selection isn't honoured by the TraceViewer itself yet... coming soon :)