Handling of Enter-key

[joho1968]

To some extent, this is related to #168, but it's not the same.

If I have a list of clickable items that, once clicked, open a Tingle modal, the link is still active (if no other element in the modal receives focus). If I hit the key, the browser's default behaviour is to act on the clickable item again, thus opening another modal (depending on how it's implemented of course).

Using this.blur() in the event handler will, of course, also work. But somehow I think Tingle should handle this better as it's a "modal".