DumpedPrivateKey,BIP38PrivateKey: inline PrefixedChecksummedBytes

[msgilligan]

This is a draft because:

a. PrefixedChecksummedBytes is not removed yet b. The tests in PrefixedChecksummedBytesTest should be replicated in DumpedPrivateKey & BIP38PrivateKey.

[schildbach]

I think that's too much of separation. It makes sense to handle both standards for encoded private keys within one class hierarchy. However, at some point I'd rename the base class.

[schildbach]

I think this is now obsolete?

[msgilligan]

I think this is now obsolete?

Yes. Closed.