Improve remove/add button visuallization

It is not easy to distinguish which add/remove button is for which sub-category when there are many categories in an asset (such as a big confusing dataformat). This problem should be addressed properly. Maybe if we have different shades for the editor objects (see #235 (closed)) This problem is solved automatically but there might be a better way.

Also at the moment the add button in the algorithm object is on the left but in the dataformat objects is on the right. The decision is to move all of them to the right.