Add integration with Apache Shiro

[Apache Shiro](http://shiro.apache.org/) is a Java security framework.  This pull request adds a basic integration between WAFFLE and Shiro.  It supports username and password authentication, and provides a good base for later enhancements to add negotiate support.  This feature was requested on the Shiro issue tracker as [SHIRO-385](https://issues.apache.org/jira/browse/SHIRO-385).