add methods to mask masks from a list of indexes
implement bezierPath in OSIPathExtrusionROI
add mask accessor
Merge pull request #19 from spalte/maskAccessor

Add mask accessor to OSIMaskROI
Merge pull request #18 from spalte/OSIPathExtrusionROI

Implement bezierPath in OSIPathExtrusionROI
Merge pull request #17 from spalte/maskFromIndexes

add methods to make masks from a list of indexes