Added several missing NULL-checks.
Reduced restrictions on building Edge-Edge and Edge-Vertex length dimension.
Added empty constructor for more straightforward initialization from vdimension command.
The following classes and their subclasses within AIS package
have been moved to new package PrsDim and renamed:
- AIS_Relation -> PrsDim_Relation;
- AIS_Dimension -> PrsDim_Dimension,