Removed underscore properties in annotations.

Closes #75.
> Note that I don't like this myself, but I wasn't able to figure out a better way to do this. In my opinion, annotation setting names and elasticsearch setting names should match, so it's easier to understand for end user. Instead of converting this from underscore to camelCase and back to underscore again, I removed the properties and store them in array. Please note that we would have to use annotation to define properties and constructor either way.