Shortcut to toggle thumbnails.

⚬ PROBLEM:
There is no way to easily toggle sidebar thumbnails without opening extension settings at the top bar. There is also no way to remove home screen thumbnails at all.

⚬ SOLUTION:
Implement a customizable shortcut that allows the toggling of sidebar thumbnails, as well as home screen thumbnails.

⚬ ALTERNATIVES:
Implementing a set shortcut that does this, but this would be inferior to a customizable shortcut.

⚬ RELEVANCE / SCOPE:
I often find that when I am studying/listening to music, I like to turn my thumbnails off. However, for general purpose usage, I like to keep thumbnails on so I can better select an enjoyable video. I believe that many people would agree, considering the popularity of a thumbnail removal option in a lot of different extensions.

⚬ "SIDE EFFECTS":
There should be no adverse side effects that aren't already present in any of the other customizable shortcuts that are already implemented.

⚬ CONTEXT:
(Discussed above in RELEVANCE / SCOPE)

The issue names no files, tests, or entry points. Start by tracing the existing customizable shortcuts and the controls for sidebar and home-screen thumbnails. Done means a user-configurable shortcut toggles thumbnails in both areas without opening extension settings, with behavior checked against the project's existing shortcut behavior.