Use separate types for storage

[rrrooommmaaa]

as discussed in #1640
for example, Key shouldn't be stored with usable, expired etc.
KeyInfo shouldn't be stored with passphrase

[tomholub]

We do actually store pass phrase, however I think we store it in a separate place, not in KeyInfo. You'll need to have a closer look at the savePassphrase and loadPassphrase methods. They use either session (temporary) or extension (permanent) storage.

[tomholub]

I'll take this on as a part of the currently reviewed PR #3213

[rrrooommmaaa]

@tomholub We also wanted to replace Key in Contact with another type, so we calculate usableForEncryptionButExpired etc. at the moment of loading.