Support for GetWinningBakersEpoch and GetFirstBlockEpoch.

[td202]

Purpose

Add raw command support for GetWinningBakersEpoch and GetFirstBlockEpoch.

Changes

• Parsing for EpochSpecifier common to both queries, which allows specifying the epoch by block hash, or by genesis index and epoch number.
• Raw support for GetWinningBakersEpoch.
• Raw support for GetFirstBlockEpoch.

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.