Crypto.DH: Renamed the DLDHE constants to FFDHE for clairity.

The DLDHE draft has been renamed FFDHE. As these constants aren't yet
used anywhere, rename them accordingly.

Also updates the references for the constants to the latest drafts
where they are defined.
SSL.Constants: Updated constants from FFDHE draft 4.

Negotiated FFDHE Parameters for TLS draft 4 (and 3) replaces and
removes some groups and renumbers some constants.

Also adds the FFDHE_GROUPS lookup table.
More const. That should be all prototypes up to date.