This commit adds two separate modes for defining angular spacing between
elements in the PD's Polar Pattern:
1. Overall Angle - which behaves exactly like it behaved before,
2. Offset Angle - which allows user to specify separation angle between
consecutive elements.
This change is analogue to that introduced for LinearPattern in previous
commits.
- remove StdDirection,StdAxis and StdMirrorPlane properties
- support sketch H_Axis, V_Axis, N_axis as valid references in patterns
- polish reference selection gui (unified for standard axes and custom references)
