fix #434: dont fetch price-info too often

[martinklepsch]

QA NOTES This change has no user facing effect. It changes how we fetch price data for our background jobs. Previously everytime we wanted to know the USD equivalent of some bounties tokens we made a request to some API.

This caused us to get rate limited as described in #434.

This change modifies our code so that we cache the conversion rate for 5 minutes. If you watch the logs on testing you should see log messages like

:SNT: Getting price-data from CoinMarketCap (token-id status)

appearing once every 10 minutes or so. You should not see these messages in quick succession.

[vitvly]

Why do we use edn/read-string instead of read-string?

[martinklepsch]

@siphiuel try this in a repl:

(read-string "#=(clojure.java.shell/sh \"echo\" \"hi\")")

see https://clojuredocs.org/clojure.core/read#example-542692d5c026201cdc327056

[vitvly]

@martinklepsch I see, thanks.

[churik]

Environments

• Ethereum wallet used: MetaMask
• Browser: Chrome, Firefox 58, Safari 11
• Operating System: macOS High Sierra 10.13.3

Tested functionality

• Contract deployment;
• Bounty funding - info updated on "Bounties", in GH bot comment