Key signature and wallet address get functions added to Public key (#144)

* small fixes

* gofmt

* fix in raw tx build

* fixes after review

* balance getter interface

* moved address and signature calculation to public key

* errors handling

* PublicKey() returns PublicKey instead of bytes slice

* fixes after review

* fixes after review

pkg/wallet/account.go

@@ -103,7 +103,7 @@ func newAccountFromPrivateKey(p *PrivateKey) (*Account, error) {
 	}
 
 	a := &Account{
-		publicKey:  pubKey,
+		publicKey:  pubKey.Bytes(),
 		privateKey: p,
 		Address:    pubAddr,
 		wif:        wif,