Temperatures are sorted and de-duplicated

When adding a temperature to one of the dropdown lists, the temperature
is not added if it is already present, and the list is sorted
Version 0.98 with better multi head support

Filament calculations are now correct when sing multiple extruders
(needs 078d-dc42 firmware)
Added ability to display info on gcode files
A head can be selected by clicking on it, and the active head is
highlighted
Added an extrusion factor slider for a second extruder
When setting head temperatures, don't repeat the T1 or T2 command if the
correct tool was already selected