[Dist] Major changes

- Create @mixin font-smoothing()
- Update button padding 12px 20px => 10px 20px
- Update $height-input-default 39px => 40px
- Update .btn-group + label styling to reflect that of a .btn
- Remove linear-gradient() on .select
- Remove %font-smoothing-antialiased
- Use @mixins to cut down on LOC