fix showing/hiding of elements for colorbox

This PR fixes the off-screen scrolling with a long file-list-container and a short sourcecode-colorbox.
The effect was that, once one is finished scrolling in the colorbox, the scroll would go past the box, and continue to scroll into a big black area, which was supposed to be the file-list-container (but it is black because of the colorbox).

Basically once the colorbox is displayed, the all file-list-container are hidden, and redisplayed after the colorbox is closed. This eliminates the black area underneath the colorbox and eliminates the off-screen-scrolling bug.

Because some code with comment was already in there (but at the wrong place) I think this behaviour was intended, but somehow buggy...