removed all dojo/on references fixes #363

I'm removed all dojo/on references in the files mentionned in #363 

- Note that in [List.js](https://github.com/ibm-js/deliteful/pull/384/files#diff-6de834fe8c8b92d25c133e8b8b06d4b9L236), I didn't convert the dojo/on() to a widget.on() but rather removed it altogether after discussing it with @sbrunot. The reason exposed by the comment above it no longer stand. 
- I didn't find an easy way to convert the [on.once()](https://github.com/ibm-js/deliteful/pull/384/files#diff-46c2d2785e39b8aece88be7198e1dafeL269). I'm not very satisfied with the current workaround, feel free to suggest a better way.