Removed whitespace when collapsing columns for mobile/smaller devices

[koenigderluegner]

This PR fixes issue #759 The idea behind this is so use a similar effect like the masonry one. It is not exactly the same effect, that's why the classes are called .fake-masonry-*.

Unfortunately the linter doesn't pass, because the master branch is not clean. I avoided to touch files which don't belong to this issue.

Wide viewport:

2-Column-View:

Single-Column-View