Fix rendering of categories and parent categories on the board [4/2]

[caldi5]

Make sure that every category added to a parent category is next to each other

[Icepool]

I’ll make sure that it’s rendered in the right way.
As we decided that parent categories are forced to be applied only to neighboring categories the code will render it with that assumption in mind.
An issue has been created for the backend category and parent category logic, issue #154