Add CSR utilities class CsrUtil.

[serac]

Provides useful capabilities for reading CSRs in various formats:

1. Get common name(s)
2. Get subject alternative names
3. Get signature algorithm name
4. Get key length
5. Generate CSR given keypair and names

Can also encode a BC PKCS10CertificationRequest type into PEM, which is the most common encoding in our experience.

Resolves #65

[dfish3r]

Looks good. Recommend adding @throws javadocs to your util class methods to describe all the conditions where you explicitly throw.