[Closed for Cosmos-SDK redundancy; Version-unspecific] Querier: Use an uncommittable CacheContext so that no querier function can make persisting changes to the KVStore

[Closed for Cosmos-SDK redundancy]

[Version-unspecific]

This is prompted by, but does not close, #1883
'/thorchain/inbound_addresses uses current-version GetFee to calculate historical outbound fees'.

I currently do not know whether there is code elsewhere that makes this redundant;
my aim is that no function called within a querier function
(whether BeginBlock/spawnDerivedAssets/churn or otherwise)
is capable of accidentally making changes to KVStore values for historical blocks.