Linear advance is reset by filament start gcode after a toolchange. However, not all moves to the wipe tower
end with a toolchange (brim, empty grid) and it would therefore disable linear advance until the next toolchange
This should solve https://github.com/prusa3d/PrusaSlicer/issues/2770
The initial priming now does not assume anything about bed width and always uses the space it has
In case of circular beds it places the priming lines along the diameter
Custom beds are not supported (they are treated as circular with no extra checks whether it is sane)
Slight refactoring of the WipeTower class (constructor now gets reference to PrintConfig and not the individual values, same with set_extruder). This was legacy from times when the wipe tower was meant to be abstract and independent on the rest)
