Use ellipses to truncate long constraint values at responsive breakpoints

[cbeer]

Fixes #925, maybe, @jronallo?

@jkeck, I saw we were truncating values in searchworks. Do you think these values are close enough to searchworks, or could they use some tweaking?

For reference:

// Extra small screen / phone
$screen-xs:                  480px !default;
$screen-sm:                  768px !default;
$screen-md:                  992px !default;
$screen-lg:                  1200px !default;

[jkeck]

@cbeer I think we're doing truncation that is not necessarily tied to breakpoints (should theoretically work under any viewport size) so we should be fine with this.

[jcoyne]

Looks 👌 to me.

[cbeer]

Oh, and I should add: there's a mouse-over title with the untruncated value.