Introduced shortcut clearfix mixins, so that clearfixing from media queries becomes possible without using the inconvenient main mixin

Sometimes it's necessary to apply clearfixes from inside media queries. But currently Toolkit offers handy clearfix shortcuts only in a form of extendables, and SASS does not allow extending from media queries.

Using the main mixin is kinda burdensome due to the fact that a never used argument goes first and you have to either provide the first argument (`@include clearfix(false, 'micro');`) or provide the name for the second argument (`@include clearfix($direct: 'micro');`).

So i added a shorthand mixin for every clearfix flavor. Now it's possible to do simply `@include clearfix-micro;` without any arguments and even parentheses.

It gets even better in SASS syntax:

```sass
.region
  @extend %clearfix-micro

.block
  @media (min-width: 400px)
    +clearfix-micro
```

PS I think that SASS should allow extending from media queries by simply declaring extendable classes inside CSS media queries. I don't see why that's impossible. Are you with me?