Allow Captions to always display

This is a new feature request.

I'd like to be able to always show captions on galleries. I can kind of trick this with `.tiled-gallery-caption { display:block!important; }` but there's still a flash of "blip" if I hover over the image.

The reason is that hovers aren't very mobile friendly, you end up having to tap twice (once to display caption, once to slideshow). We have a high number of mobile users on posts with galleries (as they're relevant to an event - think WordCamp Day 2 Photo Post where everyone is checking it on their phones). That said I recognize this is a pretty one-off request, and I'd be perfectly happy with a filter here :)