Adding 'as-of' to transaction APIs, reducing number of back-end calls, fix to network-mode selection for ohledger.

[1] Return values from getTallyDollars(..), getTally(..), getTransactions(..) changed to return wrappers `{'tally':.., 'transactions':.., 'as-of';..}

This allows returning the new 'as-of' value which can be passed back into the GET /get-transactions remuneration API to get the same results. Use of the as-of leverages a cache which allows your back-end to hit it a lot more often at higher API rates.

[2] To further reduce traffic and load, the ledgers.js library no longer calls the https://rates.overhide.io service directly. The remuneration APIs have a new 'tally-dollars' query parameter that do the conversion in the back-end.

[3] A major bug introduced in 4.1.0 is fixed: ohledger or ohledger-web3 imparter could only create PROD Stripe.com transactions (not test).