Common_Engine: Centralise methods for IElementXD's

#### Description:

We have several duplicate methods in different discipline/repo's for creating elements (e.g. IElement2D panels). Would be great to centralise some of these in the Engine (is Common the right place - or are we moving IElement methods?). As a starter for 10:

**IElement2D**
- Rectangular - creates a 4 sided panel, in a (defaulted) cartesian coordinate system;
- Vertical - creates a panel in cartesian Z;
- VerticalRectangular - creates a 4 sided panel in cartesian Z;
- AddOpening - I initially thought we could remove this from Environment object and just use 'set property' but I suspect this has been added so you can append openings to a panel (instead of replacing the list)? It made me think we might want some form of 'append' alongside SetProperty for this type of case. Could be tricky with nested lists though.

Thoughts/comments appreciated!