Bootstrap Thumbnails broken in Isis

[Bakual]

Steps to reproduce the issue

Take any extension which uses the Bootstrap Thumbnails feature (http://getbootstrap.com/2.3.2/components.html#thumbnails) and see how ugly that looks in staging.

As an example you can use my component SermonSpeaker (eg http://www.sermonspeaker.net/download/sermonspeaker-component/sermonspeaker-component-5-5-4.html) and in backend go to "Extensions -> SermonSpeaker). That brings you to a "dashboard" view using Thumbnails.

Expected result

Actual result

System information (as much as possible)

Joomla 3.6.5 vs staging

Additional comments

I think this comes from #12643.
That PR added a block to restyle thumbnails here: https://github.com/joomla/joomla-cms/blob/staging/administrator/templates/isis/less/template.less#L1523-L1692

I think those rules need a id or class prefix so they only apply to media manager related output and not all thumbnails in any extension.

[Bakual]

@ciar4n Can you have a look at this?

[ciar4n]

Thanks @Bakual I'm off the radar for the christmas but will sort this out in a few days. As suggested I'll give the media manager a unique class regarding #12643.

[Bakual]

See also #13383 (Install from Web) where this is broken as well. So we even have a place in core.

[zero-24]

There is a PR thanks @ciar4n at #13406