Api To Get Block Given Hive Block Number

[Rishi556]

Creates a method to get a engine block given a hive block number(or nothing if one doesn't exist for that particular hive block).

[bt-cryptomancer]

I think the name of this new API call is a bit misleading. getHiveBlockInfo sounds like we're getting information about a Hive block. Can we call it getBlockInfoByHiveBlock instead? Or maybe getBlockInfoByHB to be a little less wordy?

[Rishi556]

I named it getBlockInfoByHiveBlock since none of the other calls have abbreviations and I didn't want to change that style.

[bt-cryptomancer]

Looks good, thanks! Will include in the next release.