Fix the developer experience for updated npm packages

[slifty]

Right now our docker image for web-app will install npm packages on build, but it will NOT update them as we make changes to them.

We should either (1) explicitly document how to update packages, or (2) have docker automatically run npm i at appropriate times, or (3) some other idea.

There are pros and cons to both, but (1) would be better than now, and (2) could even be as simple as adding npm i to the startup script so at least when docker starts it loads the latest versions of packages.