Add Autoprefixer to easier vendor prefixing

[Autoprefixer](https://github.com/ai/autoprefixer) uses CanIUse.com to append appropriate vendor prefixes depending on the [browser range](https://github.com/ai/autoprefixer#browsers) you need to support

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- Cleanup quoting and spacing in Gruntfile
- Autoprefixer formats the files to similar to the Ruby Sass bracing placements