Upgrade Bootstrap

[jasonaowen]

We're running on an old version of Bootstrap, a framework for and default set of style rules; currently we're on the 3.x series of releases.

Unfortunately, the upgrade to 4 is more complex than changing the dependency; we'll need to update some of our rules in some way. Right now, with the latest release and no other changes, I'm getting this:

The photo is left-aligned, and there's a large white box covering most of the content area.

Figure out which of our rules we need to change to be compatible with Bootstrap 4 (or 5, if a stable release is out by the time this work is done), and upgrade our dependency on Bootstrap.