fix pencil tool bug blocking odd reverse stands

also make staple-strand active helix
new cpx file format

stores fromStrand and toStrand direction (forward = 0, reverse = 1)
old: [fiveVH, fiveIdx, threeVH, threeIdx]
new: [fiveVH, fiveStrand, fiveIdx, threeVH, threeStrand, threeIdx]
disable auto raster
draws nicer arrows

alpha indicates noStrand (0.1), strand (0.3), or hasXoverAt (0.9)