Fix existing sample data files to conform to Data Standard 2.1a RFC

Summary of outcomes for Data Standard 2.1

• Problem Addressed: Sample data files no longer validate following updates made for 2.1a RFC. Additionally, a number of pre-existing bugs in the sample data prevent the data from loading properly.
• High-level Reasoning: Sample data should be updated to appropriately reflect changes made for 2.1a.
• Changes Made: Updated sample xml files to validate against updated schema; Corrected pre-existing bugs reported as subtasks below

Original ticket description follows:

The task is to update the sample data files (https://github.com/Ed-Fi-Alliance/Ed-Fi-Standard/tree/development/v2.0/Samples/Sample%20XML) to conform to the 2.1a RFC data model.

The goal is to prepare the XML files such that they will load against an Ed-Fi ODS that implements 2.1a (though no such ODS exists today). The files should conform to XSD definitions generated by MetaEd operating off the 2.1a data model spec.

A number of updates were made to sample data files as part of the 2.1a RFC work, but some updates were likely missed.

Also, we should not create new data files for new entities - just fix existing data files. (See also DLP-123)

This is the task that will be used to merge in the updates to the Data Standard repo.