Level page redesign

[Klona13]

Introduction of tabs and less buttons in the sidebar. Some actions will be transferred to individual tabs.
Overview will have the images and description

For the walkthrough tab, we get rid of the modal and have everything needed in the tab itself.

Other tabs will be discussed in their own ticket. #388 #389

[Klona13]

This happens with infinite scroll enabled @rr-
The spacing between column disappeared.

[Klona13]

Text walkthrough update button asking for a URL, clicking on it shows that modal too @rr-

[Klona13]

I checked the separate walkthrough page, and this text appears twice now:

[rr-]

@Klona13 fixed both issues