Re-evaluate sideEffects flag values

[vidartf]

I recently read in the webpack docs on tree shaking:

components/Breadcrumbs.js: No export is used, not flagged with sideEffects -> exclude it. This also excluded all dependencies like components/Breadcrumbs.css even if they are flagged with sideEffects.

The current values for sideEffects set in our package.json files assumed that imports from a file would be checked independently for side effects, due to previous wording in the docs (mea culpa). As such, we should change to only use sideEffects if we are sure that nothing in that package/file, nor its dependencies, have side effects.