add support for signing messages in compressed format

...this is the standard way to sign messages in bitcoin-qt. Note that the
format of a compressed signature, for messages, is quite distinct from DER
format, which is used in transactions. This commit also adds support for
recovering the public key from a signature, which is necessary for this. The
code for public key recover is taken from bitcoinjs-lib.
setting networks.livenet as the default for WalletKey
Merge pull request #475 from maraoz/add/AuthMessage

adds AuthMessage and fixes browser tests
Merge pull request #478 from manan19/walletkey-params

setting networks.livenet as the default for WalletKey
Merge pull request #459 from ryanxcharles/feature/message-signing

add support for signing messages in compressed format
paypro: example - add another higher output to the server outputs.
Merge pull request #481 from chjj/paypro_server_outputs

paypro: example - add another higher output to the server outputs.
k should be 32 bytes, not 8 bytes

This is a bug with security implications. It is much easier to guess the value
of k within a 64 byte range. This would lead to compromised private keys.

The cryptography interface of bitcore is extremely poor. I recommend:
* Get rid of the C++ code, since it makes everything more difficult with little benefit
* Refactor all crypto, and have easily auditable bignum, point, ecdsa, and key classes
* Then actually audit the crypto
Merge pull request #482 from ryanxcharles/bug/k-too-small

k should be 32 bytes, not 8 bytes
Add BIP21 implementation
Add validation of required arguments for future use
paypro: example - use GET method for first paypro request.
Merge pull request #484 from chjj/fix_paypro_example

paypro: example - use GET method for first paypro request.
Skip BIP39 tests on Travis
bip21: use RegExp.exec instead of String.match.
bip21: use triple equal for consistency.
bip21: check for arg `r=` and set merchant.
Merge pull request #1 from chjj/feature/BIP21

Feature/bip21 - some changes
bip21: fix regex parse error.
Merge pull request #2 from chjj/feature/BIP21

bip21: fix regex parse error.