append_elements: using Array.prototype.forEach over elements object

Intended to address [Issue #115](https://github.com/rnmp/salvattore/issues/115) details of the fix in [my comment here](https://github.com/rnmp/salvattore/issues/115).

I ran the default grunt task but it looks like there were some changes from a previous commit that hadn't yet been built, so I'll just leave it as is for now.

I haven't tested this fix thoroughly, but it solves the issues that were seen with Infinite Scroll. As I said in the comment for the issue, I may of missed the point entirely, I'm open to that possibility :)