Better handling for "Transaction Indexing is in Progress"

[0xOmarA]

In #32 we implemented a solution to the "Transaction Indexing is in Progress" problem where we keep polling for the transaction receipt for a period that doesn't exceed 60 seconds.

However, when running all of the tests in parallel we have observed that the Geth transaction indexer sometimes lags behind and we fail to get the receipt in 60 seconds.

It looks like we might need to increase this polling period from 60 seconds and into something more generous. One option would be to keep polling for the receipt with exponential backoff so long as we keep getting "Transaction Indexing is in Progress" back from the node for that particular transaction.