enable cylindrical and cone sectors (pies) by adding sectorAngle

add sectorAngle to CSG.cylinder that defaults to 360°.
fix broken cylinder.properties.facepoint and add new one:
rename to facepointH and facepointH90 to avoid confusion
Merge pull request #43 from bebbi/cylindersegment

enable cylindrical and cone sectors (pies) by adding sectorAngle