Programmatically generate UI screenshots.

[elsehow]

Documentation should have screenshots for UI flow.

Ideally, these screenshots would be generated programatically by a build process. This would keep the screenshots up to date even as the UI changes.

In the build process, some code should describe how to achieve the desired application state. Once the state is reached, the screenshot should be generated and added to img/.

Ideally, the actions that describe how to achieve the app state could be parsed to produce dynamic natural-language "steps" for the documentation.

[elsehow]

Storybook support would make this easy. Blocked on DA0-DA0/dao-dao-ui#155.