Add alpha angle property to StrucutralCurveMember object

[sonkaste1]

The alpha angle is quite a common property in various analysis software. It is used to adjust cross-section rotation without rotating LCS of a member. The image below is from SCIA. Covering the alpha angle as a property of SctrucutralCurveMember will extend the data transfer capabilities and reduce data loss. For example, purlins might be properly aligned with the roof plane thanks to alpha angle value.

To do:
New property "Alpha angle" for StrucutraCurveMember with unit "degree". Not required value.