Fix for buttons of Select and Taxonomy/Category fields.

 * Fix typo in `bnt-info`, fixed to `btn-tertiary`, because `btn-info` might be too _flashy_.
 * `btn-mini` should be `btn-xs` in Bootstrap 3
 * No idea what happens with the margins, might want to refactor that out in the future.

TODO: In general, check the Kitchensink page and clean things up (i.e. make things a bit more aligned and uniform).