SidechainHistoryStorage, SidechainHistory data retrieving methods naming

[i-Alex]

In SidechainHistoryStorage, SidechainHistory and other places when we want and expect to retrieve an instance of A by some B, we should have a method: def getAbyB(b: B): A That should return A or throw an exception.

When we expect that A can not exist for existing B, we should have a method: def getAbyBOption(b: B): Option[A] At the moment such a method names are not consistent. Need to review and change in all places, where is needed.