BG-3196 Rename BaseCoin.prototype.deriveKeyWithSeed
BG-3196 Rename BaseCoin.prototype.deriveKeyWithSeed

Summary: Renamed to deriveExtendedKey and added short function description

Reviewers: bigly, thomas

Reviewed By: thomas

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D7753

BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS