Update the admin page style

[poppastring]

It is a long page and there are new controls that might make this a bit easier to manage.

[clemensv]

I think outside styling should generally be easier. I intentionally kept the styling model simple and specific in the original, only using and handful of config*Style classes for the element and when you search the original code base, you'll find that those styles are only used in EditConfigBox. You've used classes provided by bootstrap directly and those are more numerous and less specific and thus a bit harder to target in a theme.

I would try to make all fixed HTML as generic as possible and throw all the direct references to bootstrap out and then target elements or groups of elements with specific stylesheets for theming. SASS might be helpful here because it can extend/alias fairly easily.

(Mind that all my web skills are ancient and I might quite well be wrong)