SAK-28122

Solve the problem of ShaUtil not generating NIST-style (i.e. cross-platform) 
Hex strings.

Rename org.sakaiproject.basiclti.util.ShaUtil to org.sakaiproject.basiclti.util.LegacyShaUtil
Introduce org.sakaiproject.basiclti.util.PortableShaUtil 
Add/modify necessary unit tests

This has no dependencies outside of basiclti



git-svn-id: https://source.sakaiproject.org/svn/basiclti/trunk@315714 66ffb92e-73f9-0310-93c1-f5514f145a0a