States for contracts

[Teolhyn]

We should add states to pools. For example in the event of price data going stale, anything health factor related (e.g. making loans, paying loans, liquidating) should not be allowed. Adding collateral should still be ok as that will always increase health.

[Teolhyn]

Currently states have been added, but the logic behind changing them has not been implemented. For example we must change from healthy -> restricted if price data is stale.