Share more code between plugins and between widgets/controls

[reefdog]

There's a lot of duplicated code across the two plugins (#5 and #6) and, within each plugin, between the widget (user-facing) and control (app-owner-facing) sections.

We should look into what tooling/packing we can easily make use of that won't blow up BuildFire but will let us share more assets.

[reefdog]

Already surfaced: there's a plugin template for using Webpack, which may certainly be useful. Reference: watch this dev environment setup video and this Create Your First Plugin video.

[reefdog]

Guh, refactoring to use datastore rather than appData makes me really wish there were more shared code already.