Build: Add Autoprefixer

- Removed manual prefixing in SCSS
- Some previous prefixes will not be in the final CSS now that the
browser support matrix was up'd
- Cleaned up whitespacing and indenting in SCSS files
Improved the plugins msic file inclusion logic
Added logic for plugins assets (images, binaries etc..)
Merge pull request #3034 from LaurentGoderre/grunt-plugins-improvments

Switch the misc task to exclusion instead of inclusion and added logic for plugins assets
Merge pull request #3029 from nschonni/v4-autoprefixer

Build: Add Autoprefixer
Merge branch 'v4.0' of github.com:wet-boew/wet-boew into plugins-multimedia-player