Code review comment for lp:~widelands-dev/widelands/constructionsite_options

Fixed the compiler warnings and made the UI design consistent. I did not convert the Stop and Launch Expedition to toggle-buttons though because it is never clear with such buttons whether the icon shows the current state or the action taken by clicking it IMHO.

By the way, when clicking the Enhance button, the window will annoyingly switch to the first tab – this is unrelated to this branch, see bug 1818857.