Add autoprefixer support

Our result CSS bundle is not being processed by autoprefixer which results in missing vendor prefixes. I suggest to add it.

Pros

• No more stylelint directives for disabling rule property-no-vendor-prefix. We have one rule for FormSelect.
• Direct usage of our CSS bundle on services like JSFiddle or codesandbox.io or in projects that consume CSS bundle directly without SCSS.

Cons

• Additional dependency
• Result CSS bundle will grow in size by 2 Kb (this is right now)

CSS bundle size comparison table:

Without autoprefixer	With autoprefixer
286225 bytes (286.225 Kb)	288688 bytes (288.688 Kb)