gt-property-ng module update

This pull request is comprised of two commits; one for code changes and one for formatting and other non-functional changes.

The first commit is an update to the gt-property-module. It cleans up the syntax to better match the ContentDataStore tutorial (rather than AbstractDataStore) and enforces directories containing property files as input to PropertyDataStore. Test cases have been updated to test/support this new functionality. Where possible, warnings have been resolved.

The second commit does not contain any functional changes to the module source code - It removes unexpected whitespace, maintains a consistent indent level, removes extraneous imports, updates header dates, and fixes a few comments.