change encryption to work on hex strings

..instead of binary, to work around an issue with bitcore/sjcl. I'm not sure
what the issue is exactly, except that encryption of binary data isn't working
correctly due to some kind of string stuff involving decodeURIComponent inside
sjcl. I haven't fully figured it out. For now I am changing the network
protocol to hex to workaround the issue.

See this: https://github.com/bitpay/bitcore/pull/416