Dropdown closes on rollout of trigger element for hover mode

Before, dropdown was only closing when rolling out of the dropdown element. Rolling out of the link itself was not hiding the dropdown.

This fixes that with a timer, clearing the timer if either the link or the dropdown element is rolled over.

Related issue:
https://github.com/zurb/foundation/issues/2524

Related fix:
http://stackoverflow.com/a/1670561/686043