Make header in Skillset fixed

[Robin481]

The skillset table is heavily reliant on the table header being there for it to make sense.

Therefore, let's make the table header sticky.

TODO:

• Make the skillset table header sticky
• Write a test for it
• Be happy
• Don't Worry

[Miguel7373]

I have looked into this and tried it. I have found that it works well with CSS, but the problem is in our header. Because the header collapses so early, the sticky position of the table header gets over it at 170% on my screen, which is way too early to see reasonable, in my opinion. If you wanted to fix that, you would probably need some JS, which I would not see as worth it.