Lena

Following issue #460, the `can_trade` function does not seem to correctly return the trading state of the `TradingPair`.

Following the [report on the forum](https://forum.catalystcrypto.io/t/accuracy-of-enigma-catalyst-data-differences-found/356), the number of candles returned by `data.history()` should not exceed the maximum number allowed on each exchange.

Currently the `block_number` parameter of thSON-RPc is a string repressing a hexadecimal 32-bytes number. A more cleaner solution is using u256 type.

Update [this test suite](https://github.com/enigmampc/enigma-p2p/blob/master/test/ethereum/eth_verifier_test.js) to use Ethereum instead of a mock.

Utilize [this](https://github.com/enigmampc/enigma-p2p/blob/develop/test/ethereum/basic_eth_test.js#L445) test which was commented out at [this](https://github.com/enigmampc/enigma-p2p/pull/178/commits/180faa3849e11e39209dea0fc0356616ac56e6d1) commit