handleMousedown prevents video controls in IE11

[adnanhz]

Issue: Controls unclickable on HTML5 video in IE11.

Steps to reproduce:

1. Add an html5 video with controls in a slide.
2. Try pressing any controls button, they won't work.

I noticed that the culprit is the e.preventDefault() in the handleMouseDown function in Carousel3d.vue. I removed it and it worked.

What's the proper fix?

Thank you.