Change keystore to version 3

* Change password protection crypto in keystore to version 3
* Update KeyStoreTests/basic_tests.json
* Add support for PBKDF2 with HMAC-SHA256
* Change MAC and encryption key to avoid unnecessary hashing
* Add tests for test vectors in new wiki page defining version 3
* Add tests for new keystore tests in ethereum/tests repo
* Move JSON loading util to common for use in both tests and
  crypto packages
* Add backwards compatibility with key store version 1