Add S3 support for grant loader file operations

[rpoet-jh]

Now the grant loader can use S3 (if enabled) for all file operations. For example, the grant-data file can be read and written from an S3 bucket if the file path is an S3 url (s3://).

The grant loader now uses Spring Resources for reading/writing the grant data, grant update timestamp, and policy.properties files. This is the abstraction that performs the appropriate reading and writing depending on the resource URL. For files on a disk, file URLs (file://) should be used, for files in an S3 bucket, s3 URLs (s3://) should be used.

[markpatton]

Looks good. Passes for me locally.