Make scooter work as a mixin library

[standardpixel]

Right now the only way to import styles from scooter is as classes. This means that the whole library will be imported if you import extend a class with one of scooters internal classes. If instead scooter started by providing placeholder classes %classname and then used those to create it's regular classes .classname, others could use scooter to extend their existing classes and not have to clutter up their markup with scooter specific class names

[lunaroja]

👍 Great suggestion!

I did this slightly differently for the grids, because they are still include because @include grid; at the bottom. https://github.com/dropbox/scooter/blob/master/scss/objects/_grid.scss#L65

For now, the only way to do what you need is to not @importobjects/_all';` and do

@import 'objects/_flag';
// @import 'objects/_grid';
@import 'objects/_list-ui';
@import 'objects/_media';

... but then you can't mixin your own. 😢