Details/summary: Removed reference to non-existent demo SCSS file.
Merge pull request #4822 from EricDunsworth/v4.0-broken-link-fixes

Details/summary: Removed reference to non-existent demo SCSS file.
Date picker: Made disabled month arrow more visually distinct from the active month arrow
Merge pull request #4824 from pjackson28/fixdatepickerarrows

Date picker: Made disabled month arrow more visually distinct from the active month arrow
Bootstrap: Switch to Sass variant

- Use the bootstrap-sass-official till the Bower package can be renamed
- Monkey patch the LESS "fadein" function till the next release where it
is fixed
- Mute CSSLint warnings that are introduced by the Bootstrap mixins