This also reverts to wx.SHAPED for the gviz packing, and specifies a minimum
size with the correct aspect ratio.

This callback is useful to broadcast the last print line sent in the form of
the parsed gcoder.Line object. We can then augment the gcoder.Line to do
awesome stuff, such as updating the print status in the 3D viewer.

This might speed up Pronterface while printing.
Indeed, as we keep adding items we keep expanding the list and Python has to
move it all the time.

I'm hunting unjustified try: except: blocks.

The icon was adapted from the 24x24 "Refresh" icon from Humanity Icon theme.

As far as I understand, a wxFrame needs a wxPanel child, but we shouldn't
reparent this wxPanel to some other container. As a consequence, I created an
initial wxPanel for the gwindow wxFrame and assigned it the previous sizer
(instead of using the gviz panel as the wxFrame's panel).
Not sure why it wasn't segfaulting on my other systems, though.