Early fan edition

note : prusa3d hasn't released their alpha6 yet, so it's not merged inside that one. But it's merged over their alpha6 tag (i don't think it will be used).

new

• solid fill pattern setting, to change the pattern of the solid fill. Should be kept at rectilinear, but feel free to experiment with it.
• rectilinear infill : now a bit better handling at connection in sharp region (try to fill the empty bits a bit more, can connect more often). I had some under-extrusion in these area, i hope i don't overshoot with these changes.
• add "filament max wipe tower speed" (filament ->advanced)
• add a bit more option to filament type, go here to see how to use them
• support : new setting to select the interface fill pattern .
• experimental sawtooth fill (idea from e3d). But i didn't test it yet, so be careful, it will print as shit.
• fan startup delay (hardware->general->firmware) to start the part cooling fan a bit earlier if possible. It doesn't jump over the previous object, so it shouldn't wreck the cooling. It can add a new option on the M106 to tell the firmware that the fan should be at this speed in X ms (no firmware support that yet).

bugfixes

• all from 1.42.0-alpha5.2
• better role for gapfill from concentric fill.