Add missing fields to stake event

Background

Block explorers show and query events based on to and from address (currently via the /v1/txs endpoint), however the stake event does not contain all required information. To get it, Midgard must make a request back to thornode's API to fetch the missing information and make a new table to store the additional non-event info in.

If stake events were more complete similar to swap events there should be no need to go back to the thornode which would result in cleaner events and less two-way coupling.

Proposed solution

For both single transaction and dual transaction stakes: add memo field, also add the to_address.

For just dual transaction stakes: also add the from_address

Chain bloat

This does cause some chain bloat and the impact is not that bad on Midgard. But if it's easy to add then it would definitely make the event handling cleaner.