Remove Bootstrap from Header and assets.toml
Remove Bootstrap JS CDN version in footer and assets.toml
Add latest Bootstrap v4 SASS files locally
Include Bootstrap JS locally
Convert Academic's CSS to SASS (mainly SASS variables + Go templating)
Convert Academic's theming system to integrate with SASS
Parse SASS in header using Hugo and convert to CSS
Minify and md5 fingerprint bundled CSS
Fix Slider widget (reuses .wg-hero but animation and `clear` removed)
Add Bootstrap files to repo so that Node is not required
See #680
Also renames Hero Carousel widget to Slider.
BREAKING CHANGES:
- widget `[header]` options removed and replaced with `[background]`
- `hero_carousel` widget renamed to `slider`
Close#948
George Cushen