Building OTCryptoPP for review. Do not merge.

Full OTCrypto implementation in CryptoPP.  Same API.

I still need to do OTAsymmetricKey for CryptoPP.

This is half-way work towards using Bitcoin compatible crypto.

Please review:

https://github.com/da2ce7/opentxs/blob/cryptopp/include/opentxs/core/crypto/OTCryptoPP.hpp
https://github.com/da2ce7/opentxs/blob/cryptopp/src/core/crypto/OTCryptoPP.cpp

Cam.
I guess the crypto libs provide it because they want to provide a ready-to-use toolkit. But the fact is that base64 encoding doesn't have anything to do with cryptography, and we shouldn't make our interfaces more confusing just because crypto libs offer that functionality out of convenience. 

For reference, the Bitcoin project doesn't use any external dependency for base64 encoding and puts the related methods in a file called `utilstringencodings.cpp`: https://github.com/bitcoin/bitcoin/blob/610a3d3a1bd171b963600c55fab715ca2aa30da3/src/utilstrencodings.cpp#L90

It's such a small function that we can justify just providing our own implementation.