Updating query server to have turnstile access

[davidterpay]

In this PR, I add

• another endpoint to the query server that will allow users to retrieve the turnstile address
• wrap the CSR response with a revenue_string value so that the revenue bytes can be converted to string correctly
• make a small fix to the posttxprocessing hook to ensure there are no nil dereferences
• add test cases for the updated query server

Testing

Run go test -v -race ./ in the keeper and types directories in x/csr.