Add missing tests (see included list)

[dcousens]

• Add tests for Transaction with no signatures
• Add/verify tests for TransactionBuilder.fromTransaction that cover the situations specified in Redundant blank signatures are added when signing incomplete multisig transaction #404
• Add tests to verify Review #411 reaching undefined signatures #415 is not an issue
• ECPair: fix modulo bias in makeRandom #447 (comment)

[dcousens]

@jprichardson you want to do this? haha

[jprichardson]

@jprichardson you want to do this? haha

Possibly. I'm still waiting for an email response from you about the project standards, protocol, etc :p

[dcousens]

All resolved, closing in favour of #460 for the last point.