added simple scaffold helical rotation indicators
Update virtualhelixitem.py

Fixed parity check.
Update virtualhelixitem.py

fixing again with a twist offset for square lattice parity error
Update squarepart.py

twist offset added to squarepart
Update honeycombpart.py

twist offset added to honeycomb part
update squarepart.py _twistOffset to display better crossover alignment in sliceview
Update README.md

Fixed installer link
Merge remote-tracking branch 'upstream/master'