Order History events in the same confirmation height.

[junderw]

REQUIRES RE-INDEX

REQUIRES A LOT OF TESTING

This should fix the ordering of history entries and transactions within the same block/tx.

I think the addition of this data to the rows might cause unforseen consequences... so it needs to be tested thoroughly.

Requires a Re-Index.

[junderw]

(Included #92 because mempool branch is broken without it)

[junderw]

The behavior of the RocksDB is relied upon in weird ways, so the biggest worry I have is a re-surfacing of the weird balance-is-off bugs...

[mononaut]

(re)tested ACK @ [3dab4c7e]

I completed a full mainnet reindex with the new u16 tx position, and everything looks good so far, including balances on a bunch of heavily-trafficked addresses.