Change default crypto provider to SCrypt

It is well known that hashes, even when salted, are weak against offline
attacks. Since adaptive hash functions are already supported, default to
the best option so that users start off with the most secure choice by
default.

Signed-off-by: Aaron Bedra <abedra@cigital.com>
Merge pull request #392 from abedra/master

Change default crypto provider to SCrypt