View to track deal activation, slashing, expiry

Essentially need a view that does:

```
SELECT
min(s.height) FILTER (WHERE slash_epoch < 0) as act_height,
min(s.height) FILTER (WHERE slash_epoch > 0) as slash_height,
s.deal_id, end_epoch
FROM market_deal_states s
JOIN market_deal_proposals p ON s.deal_id = p.deal_id
GROUP BY s.deal_id, end_epoch
```

Where for each deal it is possible to see when it was activated, when it was slashed, and when it expires. This JOIN takes way to long.

Alternatively we could add end_epoch to market_deal_states (in scope of #495 perhaps).