Videos break drop area in gallery due to variable thumbnail size

[thomaslow]

Describe the bug
In the gallery, video thumbnails are styled differently (with regards to their size) from image thumbnails. This affects the drop area of the thumbnail, which assumes a fixed width of 75px and height 105px.

You can see that the drop areas are positioned incorrectly.

To Reproduce
Steps to reproduce the behavior:

1. Import a video
2. Try to drag another thumbnail in front of the video

Expected behavior
Videos should either conform to the fixed thumbnail size, or the drop area styling has to be improved.

Release
Master