Rename auc:eGRIDRegionCode to auc:eGRIDSubregionCode

[macintoshpie]

Describe the bug or data model issue
it's technically eGRID subregion code not eGRID region code
Also, there should be only one of these codes allowed (BSync has no maxOccurs currently)

Expected Behavior
Element name should be correct, and maxOccurs should be 1

Actual Behavior
BuildingSync uses Region instead of Subregion in the element name, users can provide unlimited number of the element.

[macintoshpie]

Closing b/c we are reopening #358