Support standardized Hex format(s)

There's 2 commons hex formats at the moment
- prefixed hex strings `0x123456`
- Buffers `new Buffer('123456', 'hex')` ( ideal memory footprint )

Currently `eth-lightwallet` expects non-prefixed strings.
Maybe wrap all public fn inputs in a format normalizer fn

Start by locating the public functions in eth-lightwallet that currently expect non-prefixed hex strings and trace how their inputs are handled. Done means the relevant public inputs accept both prefixed hex strings and hex Buffers without breaking existing non-prefixed string usage; check the existing test suite for coverage.

Written by the indexing model from the issue text.