Table custom errors until a later date. Remove need for devDependencies ...

- Fixes installation when using `npm install bitpay/bitcore#v0.8` and requiring in `package.json` #650 by removing need to run devDependencies
- Stack traces are correctly reported for errors #646 by tabling custom errors, we can revisit later with #651
- When instantiatiating an HDPublicKey with an extended privatekey will return the associated HDPublicKey