Modify the btcsuite address requirement to be coin agnostic

[amangale]

In this change, a new interface 'WalletAddress' is introduced which contains the methods used by the app. The one method 'IsForNet' which is btc specific is excluded.

[cpacia]

So me, mg, and tyler talked about it. I think we're OK to remove the Params() function but at some point we do want to add in a function to return coin specific data as in #2.

Additionally, the Params() function is currently being used in ob-go to generate HD keys, but we're thinking about changing the three interface functions that take in the HD keys to accept a new MasterKey object and have the wallet implementation be responsible for deriving the HD keys from that so the derivation does not happen in ob-go and it doesn't need to know about the key derivation data in Params().

I'll add to this PR with changes we're thinking about.