Refactor `Help`

[hasezoey]

Describe what you want

This is practically just a tracker to not forget to do it.

re #691 (comment)

Do you have already an idea for the implementation?

Refactor Help list to be actually fully correct.
This implies going through all components and standardizing all keybindings (including hard-coded ones) and listing them correctly.

Additionally it would be great if:

• context sensitive help (while having playlist focused, those keybindings should be the first in the list (maybe if not the only ones)
  • Should this maybe be done in a layered / tree like approach?
• searchable help
• improve display on longer key displays to not be cut-off

[tramhao]

It looks like a whole new help system. Looks great by the way.