opentxs cli: introduce flag "--dummy-passphrase".

This sets a password callback that always returns "test", without
requiring manual input from the user at the prompt.
This allows us to call the client in automated scripts.
Merge pull request #349 from benma/dummyPassphrase

opentxs cli: introduce flag "--dummy-passphrase".
Added bitcoin-base58 library.
Use base58Check instead of base62.
Updated the bitcoin-base58 submodule.
New ID format: OT-[base58Check with version byte 0].
Renamed functions s.t. they do not mention base62 anymore.

Also fixed up some comments that are not accurate anymore.
Use the (ripemd160 . sha256) hash algorithm for identifiers.