Added Darksend high precision matching engine

Darksend is now capable of taking queue objects (which show who wants to mix what)
and looking at it's own inputs to see if it's at all possible to join their mixing
session. This plus other improvements should make Darksend much faster for mixing
coins.
Implemented KeePass Integration

More info regarding KeePass: http://keepass.info/

KeePass integration will use KeePassHttp (https://github.com/pfn/keepasshttp/) to facilitate communications between the client and KeePass. KeePassHttp is a plugin for KeePass 2.x and provides a secure means of exposing KeePass entries via HTTP for clients to consume.

The implementation is dependent on the following:
- crypter.h for AES encryption helper functions.
- rpcprotocol.h for handling RPC communications. Could only be used partially however due some static values in the code.
- OpenSSL for base64 encoding. util.h libraries were not used for base64 encoding/decoding since they do not use secure allocation.
- JSON Spirit for reading / writing RPC communications

The following changes were made:
- Added CLI options in help
- Added RPC commands: keepass <genkey|init>
- Added keepass.h and keepass.cpp which hold the integration routines
- Modified rpcwallet.cpp to support RPC commands
Refactored encryption / decryption and base64 routines
Refactored KeePassHttp protocol implemenation
Refactored keepass getlogin and implemented setlogin