Nicer contributor popovers

[bedroesb]

This PR will bring the same style and information from the contributor tiles in the overview page to the popovers at the bottom of each page:

[bedroesb]

live preview here: https://bedroesb.github.io/rdmkit/data_transfer

[martin-nc]

Looks good to me! I see the popover footer is a different colour in the Contributors' page but I think that's fine. You can't use the grey against the grey background of a "normal" page and the dark blue would be too much in the Contributors' page!

[bedroesb]

@martin-nc wow you summarized my struggle really well :D I also thought of a shade, but we don't use shades of our primary colour anywhere

[martin-nc]

If you wanted to be absolutely consistent and have a grey footer in the popover, then a darker drop-shadow might distinguish it from the grey background. I'm not sure if it's necessary, though.

[bedroesb]

@martin-nc I took now the same drop shadow as the search dropdown, but yes you are right

[bedroesb]

I guess for now I leave it like this. it is an improvement. If it bothers me I make a new PR :)