Fix saving privatekey, add onlymentions

[vicariousdrama]

• home option can now filter for events mentioning caller even if no followers using --onlymentions flag
• fixed bug in storage of private key. it should be in a format that can be consistently decoded for future calls.
• restored call to printPublishStatus in message handler

[fiatjaf]

@honza do you have an opinion?

[vicariousdrama]

getPubKey expects config.PrivateKey to be in hex format.

func getPubKey(privateKey string) string {
    if keyb, err := hex.DecodeString(config.PrivateKey); err != nil {
        log.Printf("Error decoding key from hex: %s\n", err.Error())
        return ""
    } else {
        _, pubkey := btcec.PrivKeyFromBytes(keyb)
        return hex.EncodeToString(schnorr.SerializePubKey(pubkey))
    }
}