Configure ckaneext-datagovtheme to use SCSS build pipeline

[btylerburton]

User Story

In order to properly consume new versions of CSS dependencies (ex. USWDS, Bootstrap), data.gov team wants to reconfigure the ckanext-datagovtheme to build assets in a modern pipeline using NPM and SCSS. This will greatly reduce our CSS footprint and allow us to consume new versions of USWDS with ease.

Acceptance Criteria

[ACs should be clearly demoable/verifiable whenever possible. Try specifying them using BDD.]

• [ ] GIVEN [a contextual precondition]
  [AND optionally another precondition]
  WHEN [a triggering event] happens
  THEN [a verifiable outcome]
  [AND optionally another verifiable outcome]

Background

[Any helpful contextual notes or links to artifacts/evidence, if needed]

Security Considerations (required)

[Any security concerns that might be implicated in the change. "None" is OK, just be explicit here!]

Sketch

• [ ] Integrate NPM into datagovtheme.
• [ ] Install necessary modules (USWDS, Bootstrap, etc).
• [ ] Isolate CKAN overrides into a single stylesheet.
• [ ] Remove any CSS in datagov theme that is related to USWDS components.
• [ ] Configure build pipeline to output a CSS artifact.