A preliminary pass at number_with_delimiter

This is more to start a conversation as well as provide a possible
single concrete implementation for other things that might go into
Lotus::Helpers:

- I18n
- HTML Safe concerns
I have considered this, but probably we'll get soon out of scope. There are other goods conversion gems, it doesn't create any value added for Lotus.

I'd say to keep our focus on formatters for now (eg. currency, percentages). Also, I'd add another  module to mimic Rails _"humanize"_ helpers for numbers, measurements, file sizes..