Refactor item region processing and loading

This refactoring allows subclasses to add region binding fields without having to rewrite all the loading and processing code.
Merge pull request #2 from isaacgrant/check-region-protected

make checkRegion() protected
refactor for easier subclassing of the item group dependency list
Merge pull request #3 from isaacgrant/to-string-fixes

__toString must be public as of 5.3
Merge pull request #4 from isaacgrant/item-group-delete-deps-for-subclasses

refactor for easier subclassing of the item group dependency list
Merge pull request #1 from isaacgrant/item-edit-region-binding-refactoring

Refactor item region processing and loading
prepare for release of 2.0.3
move the loading of new StoreItemRegionReplicator's into its own method for easier subclassing