Tx51 (crowdsale) version 1 accepts multiple currencies, including bitcoins

We need to specify the block number where tx51 version 1 will be turned on.

* tx51 version 1 allows 0 (bitcoin) for Currency Identifier desired
* early bird bonus no longer tied to weeks **(this change has been undone by a later commit that's part of this PR)**
* number of tokens issued limited by max Number of Coins value
* Number of Coins now a signed 8-byte integer