UP-4030: Adding ability for the Person Attribute Group Store to be imported/saved and leveraged instead of XML file

https://issues.jasig.org/browse/UP-4030

Items implemented:
- import
- runtime leveraging entities
- export

Items remaining:
- ui support

Adding ability for the Person Attribute Group Store to be imported/saved as entities and the config to leverage the imported entities instead of the xml file being statically read on startup.