Implemented event delegation for items inside bellows. 

Implemented event delegation instead of binding to individual elements. This will allow dynamically added items to work without rebinding. Also refactored the CSS classes into their own object, so the code is inline with the selectors object. Added a few comments. 

Status: **Ready to merge**

Reviewers: @kpeatt @tedtate @donnielrt 

## Changes
- changed standard event binding on individual items to delegated event binding on bellows parent
- refactored CSS into object, and renamed properties
- added comments

## How to test-drive this PR
- checkout this branch
- `grunt test`
- `grunt serve`, ensure no linting errors, and check the examples - specifically test the default example, and bellows within bellows