Tidying up

[MilkywayPirate]

Purpose

Tidying up and fixing a few json deserialization bugs.

In particular MintDistribution was not properly deserialized.
Introduced some wrapper types for BLSKeys and VRFKeys which are used when generating baker keys.

The flow of baker keys also changed slightly, such that one must call BakerKeys.createBakerKeys in order to create the keys and then these must be supplied to TransactionFactory.newConfigureBaker.

BakerKeys also exposes a createBakerCredentials helper function for writing out baker credentials that a node can be configured with in order to participate in the baking committee i.e. start baking.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.