Add command to check key/message security properties.

[ni4]

Description

There is some demand to check OpenPGP keys/messages for enough level of security, i.e. report weak algorithms, hashes, weak algorithms in preferences, too small key sizes and so on.
This could be implemented as command rnp --security-check <keyid|keyfp|filename|use stdin for input if no parameters>

See the discussion here: https://mailarchive.ietf.org/arch/msg/openpgp/ihpeJXJCNvVbYrEooYOAWwqFAr8/