Allow customisable keyboard shortcuts

[Dominic-DallOsto]

This would be the real solution to #9, and would also allow users to fix #30.

Ideally, like vscode does, have a space where the user can click, press a key, and this would set the key combination.

Need to make sure keypresses involving the Win (or Command key on Mac) are correctly handled so that they work as a modifier, or else tell users that these keys are not available

[kzssc]

+1
relatedly (on a mac), in pdf viewer, the plugin hotkeys are overridden by the annotation tools. One cannot use hotkey to change the read status when in pdf viewer, only in the library.