Add time, height, consensus to block context

[Bushstar]

Summary

• Time and height should have been defined in block context instead of transaction context. This PR starts moving them to from transaction context to block context. To keep changes to a minimum this PR adds them to the block context and retains them in transaction context as aliases. This prevents a large changeset in one go which is then safer to implement and easier to review.

Implications

• Storage

  • Database reindex required
  • Database reindex optional
  • Database reindex not required
  • None

• Consensus

  • Network upgrade required
  • Includes backward compatible changes
  • Includes consensus workarounds
  • Includes consensus refactors
  • None