enabled address generation using bip39 mnemonic

[UVNishanth]

• modifications:

1. client/miner has password to add salt for address generation
2. blockchain has a mnemonic parameter and generates address for clients passed to its createInstance() using that mnemonic
3. Late participants get the blockchain instance and use its mnemonic property to generate their address

• not-clean-code:
  the blockchain isInstance might not be the best way to set late participant's address, but couldn't come up with a better solution

[taustin]

Looks good overall! I've added a few suggestions/comments. Take a look and let me know when you are ready for me to review again.

[taustin]

Two more minor fixes relating to comments, and then I think it is good to go!

[taustin]

Looks good!