add consent signature image to Java SDK

Added consent signature image and getConsentSignature API. Updated ConsentTest accordingly.

This builds and all tests succeed when run against my local dev box. Note that the getConsentSignature is in Devo but not yet in Prod.

Will run "mvn clean compile test" one last time just as a sanity check.
Totally agree with this. LocalDate would be better (I couldn't find anything more appropriate in Joda).