Cleaned up javascript code

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3
| Fixed tickets | n/a

1. Reused variable `emailList` which is best practice and easier to read
2. Removed `return false`. There is no use for it in this context and many consider it to be bad use as well. For example: http://fuelyourcoding.com/jquery-events-stop-misusing-return-false/
I think `e.preventDefault()` is easier, since its naming is clear about what it is doing: preventing the default behaviour. `return false` might be intuitive to JS developers, but it clearly isn't if you aren't used to program in JavaScript.

Furthermore, using it is consistent with the jQuery examples in the form collections cookbook (I think we might need to make them even more consistent).