Add restrictions to replace and create series

Containing fixes to teknico's code review comments
So, I think that instead of testing the same errors exercising both CreateSeries and ReplaceSeries we should do so only once exercising PutSeries as that's where the errors actually come from. It avoids duplication and, by doing so in a single table-driven test we can more easily ensure they're actually testing what we want, unlike TestReplaceSeriesTooFewKeys above ;)

https://github.com/monetas/btcwallet/pull/41