add support for signing/verifying messages

This adds a new Message class with static methods for signing and verifying a
message the same way as bitcoind. (In a nutshell, messages a prepended with
"Bitcoin Signed Message:" before being hashed and signed).

There is one important piece missing ... verifying a signature with an address,
and not a public key. I have not yet implemented this because the cryptography
interface of bitcore does not allow me to derive the public key from a
signature. This will need to be added before verifying from an address is
possible.
add Message to browser build and tests
add extend dependency, use to extend defaults with config in PeerManager instead of overwiting all
Merge pull request #270 from ryanxcharles/feature/sign-message

WIP: add support for signing/verifying messages
add support for peer discovery to PeerManager and example of usage to examples/
resolved merge conflicts
simplified example for peer discovery, added some debug output to discoverPeers(), made Peer reference the connection created from createConnection()
fix networks var in discoverPeers() to match what might be imported
some aesthetic changes
fix example
update version to 0.1.12

Major updates since last version:
* SOCKS5 support
* Move classes to ./lib
* Message signing/verification
* Many minor updates
setup connection pool and auto handling of bad seeds
update example, added log statements to status check in peer manager for showing how many good peers there are
Added Electrum.js which allows Electrum style key derivation
Electrum.js specified what is supported for now
Electrum.js: wrote some tests
Electrum: removed dead code
add Electrum to browser build and tests
Merge remote-tracking branch 'gordonwritescode/feature/peer-discovery'
Merge remote-tracking branch 'olalonde/electrum'