improvements for mode "Player size: Full window" - header and scrollbar

[Doosty]

SHORT Table	(Summary)
Problem	im frustrated because mode "Player size: Full window" could be improved for the best possible immersive experience, specifically scrollbar is not needed and there is no good option for the Header - i either have to use Hidden or Hover which still uses topmost real estate
Solution	add feature "Header position:Below player on video page" and "Scrollbar:Hidden on video page"
Alternatives	this userscript does it perfectly https://greasyfork.org/en/scripts/811-resize-yt-to-window-size , but i would very much like to use your plugin instead since it has a bunch of other amazing stuff
Scope	awesome for everyone who uses Full window mode
Side effects	none, just an added functionality
Context	my optimal viewing experience is video completely filling the browser page and video being the topmost element and still being able to use youtube search below the player. Screenshots show the functionality of the above linked script

picture 1: page scrolled to the top, video completely fills the window, scrollbar is hidden ->

picture 2: page scrolled down slightly, shows the youtube header neatly below the player ->

[ImprovedTube]

welcome @dusty071
worth thinking about as we are the nr1 source for this feature, used to be the only one.

when enabling 'full window', then "Scrollbar:Hidden on video page" could appear enabling itself, below 'full window',

• also this could be more specific and only hide scrollbars while window is not scrolled down far (like miniplayer)

header could also stay static, but page could be scrolled down little from the start, as much as the header height