Bootstrap (and its dependency popper.js) are now used from npm packages,
allowing better version control and custom building of only the required
components for both styling and javascript.
At this moment the whole styling of bootstrap is included, once the Cloud
redesign is over it will be stripped to only the used components.
Blender Cloud used main.css from Pillar
As we try to strip Blender Cloud-specific content from Pillar,
this commit brings three .sass files over to this repository.
There are still plenty of Blender Cloud classes all over Pillar,
they will be brought here over time.
