Add support for iniConfigs in config.yml

It would be nice to be able to specify the location of shiro.ini file in a dropwiard config.yml. 
See this gist for an example config.yml: https://gist.github.com/kdhindsa/2d2a505750874516f272

I tried to do it, but I couldn't get it to work. See this post on dropwizard-user google group: 
https://groups.google.com/forum/#!topic/dropwizard-user/dK_LKkQqZB0
