[TrustID-sdk] Allow DID imports from keys not belonging to TrustID

[adlrocha]

Providing the publicKey and privateKey for a DID should be enough to import a valid TRUSTID did. Right now we only support the TRUSTID DID object structure.

We should even consider the import of keys from a seed. The import process would be:

Seed --> Generate Key --> Generate DID --> Store DID