Updated SSL certificates

We've updated the certificates for SSL pinning.

Removed CommonCrypto

• Removed the dependency to CommonCrypto, so it's possible to use Carthage and Cocoapods
• Supported banks and services endpoints don't require login any more

Improved error handling

In case of errors the API sends an error object. We have changed the FigoError type to pass that through in error cases.

It contains a code identifying the error and a couple of strings describing the problem. See http://docs.figo.io/#error-handling for details.

Support for macOS

• Re-added support for macOS
• Updated README.md

Swift 3.0

We have updated the project to support Swift 3.0, older versions of Swift are not supported.