Upgrade to Bootstrap 4

[sumnerevans]

We're currently on 3. I think this is a good issue for the field session project to take on.

Notes

• We will need to remove all usage of Glyphicon. Currently, we only use it in one place, and that can be replaced with FontAwesome.

[jackrosenthal]

This might be something we can tackle before then, I would rather FS project focus on things they could learn from (rather than just converting panel and wells).

In other words, no, I will not give this to FS team.