Pulled latest master from kliment/printun and changed extrusion length
to a hidden setting. It is now saved upon change as
settings.last_extrusion and can be set as such. Also added default
extrusion length that may be used as a fall back for deploying printrun
with a different default extrusion length without having to change that
everywhere in the code.

Added "extrusion_default" to settings and made it editable via settings
file. Setting is not written back when the user changes it through the
gui.

Breaks Tabbed mode for now

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