add team pictures to the focus area pages

[davidlange6]

closes #715

[henryiii]

Can't we use standard_person_card?

[davidlange6]

that's what I started from (perhaps hard to tell that now). I don't think we would want so much space taken up by pictures on the focus area / team pages, so I made them much smaller.

[henryiii]

I've started refactoring the looping code a bit. We should be able to use find (new in 4.x) and where to clean up our loops (https://jekyllrb.com/docs/liquid/filters/), and it's really easy to add a Ruby filter for the more advanced stuff. That should be much more readable / maintainable, and is much faster (liquid is slow due to all the double looping we tend to do).

[henryiii]

This doesn't work for focus-areas that don't have projects, like ssc and ssl.