Adjust quote styling

[koopmant]

Adjust blockquote style to make quotes more obvious.

closes #3623

[koopmant]

I ended up simply adding some css.

It took me a long time to find out that there was no css being overridden anywhere. The blockquote style with a border on the left is part of an older bootstrap version (at least still there in 3.3.2).

Markdownx does not inject any css, although there is some css included for the admin site.

[koopmant]

Preview

[koopmant]

Preview:

I've opted for the primary color now, because the bootstrap gray colors are overridden in our flatly theme and that does not leave me with the dark gray that I'd like to use. (Not sure why Flatly chose to do it this way; I think it's a bit odd because this leaves a gap in between gray-700 and gray-800, see below.)
I thought about resetting the gray colors back to the bootstrap original values, but then I'd have to apply fixes for those changes as well (such as setting the secondary color from gray-600 to gray-500), so I decided to not do that.

Flatly (left), bootstrap (right). Gray 500, 600, and 700 are overridden.

[jmsmkn]

I get this when trying to merge, do not know what is going on:

[koopmant]

I see the same thing when I try it. I have not experienced this before.

[jmsmkn]

It fixed itself.