Long MOTDs overflow to the bottom of the window. I suggest to make it scrollable text.

This covers https://github.com/teeworlds/teeworlds/issues/1857 except for the server browser, which is pretty tricky because of the layout and arrow keys navigation. I'll look into that one later.

• Changed default values of the background for the scrollbar API (50% -> 25% alpha) to be consistent with the Teeworlds UI
• Fixed too high background alpha in the controls menus
• Updated list boxes to use the new scroll regions

• this affects a lot of places
• Updated the side bar in the ...