Replace global packages with npm imports where possible

[nickbclifford]

While working on #119, I noticed that there's a lot of places (progress bar, twitter, etc.) where we're using global variables imported with Angular CLI instead of importing directly from npm. This is kind of confusing, and frankly unnecessary in some places now (i.e. Chart.js has an exported module), so it would be a good idea to see if we can replace them in places.