Adjust z-index for Bootstrap modals. Don't show display hint when calling clear()

The z-index setting is too low for Twitter Bootstrap modals, resulting in tokenInput appearing to not work if one should use a tokenInput in a Bootstrap modal.

Separately, calling the clear() function triggers the display hint text to show. As calling the clear() function is done programmatically (in my case, as part of a BackboneJS render function), I do not want to trigger the display hint text. That should only be triggered when the user does something, not when another piece of code does something, in my opinion.