Add Bootstrap Support

Replaced all classes, the (S)CSS still needs work.

We decided to create a separate drowl_layouts_bs module (on Gitlab, not a Drupal.org release).
I'll finish cleaning up the module in this issue branch, and then move it over.

@thomas.frobieter close with https://www.drupal.org/project/drowl_layouts_bs → and perhaps add some documentation about the end of Foundation and the new module on the module page?