Reduce infura calls

[nicholasmueller]

• we make about 6 node calls every 15 seconds per client.
• we get this for free through a provider like metamask, but through dapp browser providers (imToken, status) we get timeouts, probably due to some kind of rate limiting.
• see what can be done to reduce these calls on the frontend, and make them only when needed (pending transactions, increase the interval when checking challenge period, etc)

[bg1156]

Go nic, Go!