Add ECC support

This pull request adds ECC support to Red October. The `passvault` package contains a variable defining the default for new password records, but existing records are unaffected. Encryption with ECC is done using ECDHE (with the P256 curve) to generate a shared key for AES-128-CBC-HMAC-SHA1, following suit with the rest of the system.

Due to the original design of the system where public key crypto is used to encrypt a KEK, existing RSA records are still usable (and can coexist with ECC records).