Project jigsaw has added support for signed module files, which like jars, allow the user to timestamp the signed code. While developing
signed modules, it became clear that some of the current timestamping code should be restructured so that it could be more easily shared
by the 2 mechanisms (signed modules and jars).
The changes in this CR include:
1) Adding a new java.security.debug=ts option for timestamping debugging
2) Moved SignatureFileVerifier.getTimestamp() to SignerInfo.getTimestamp()
3) Moved code from TimestampedSigner to a PKCS7.generateSignedData() method
4) Other misc. small changes