Building element base quantity does not have "Base" in the name

This is a bit of an oddity, but most base quantity qtos have "Base" in the name, like Qto_WallBaseQuantities. BuildingElementProxy is the odd one out and does not have "Base" in the name. Can we standardise this?

Start by locating the IFC definitions for BuildingElementProxy and the related Qto_* quantities, then compare the naming pattern used by Qto_WallBaseQuantities. Standardize the BuildingElementProxy quantity name and update all references consistently; done means the specification has no inconsistent name remaining.

Written by the indexing model from the issue text.