Make Orbit compatible with Ember/Handlebars/Metamorph

When generating the LI's to use within an Orbit component, the ```each``` Handlebars helper generates Metamorph ```<script>``` tags before and after each LI. Orbit did not discriminate the contents of the containing UL, so it applied the styles to all of the UL's children, including the script tags. This caused the slider to think it had more slides than intended.

This commit makes sure Orbit only looks at LI's, ignoring any other tags within the containing UL.