Add an object to the collection.
Uses the passed ID, or generates a new ID by generating a Unique ID, casting to a string and prefixing with the string 'obj'.
This ensures a hashed lookup (VBA collection hashed lookups are always of type string) If a numeric ID is passed, it is coverted to a string prior to key lookup. Returns the IDString used.
Object to add to the collection.
The string to use for lookup in the collection. A new unique string is generated if this parameter is empty.
id = ObjectCollection_Add(thisForm, "")