Couple more keyboard shortcuts to boost the keyboard-only workflow

A) Shift focus to "Style sources"
B) Move focus
B) Move focused instance "up or down"
C) Move focused instance "in or out"
---
This would allow for a super fast workflow to

1. Add a component to the canvas
2. Move it to the right place
3. Add styles

And couple of bonus ideas:
--------------------------
D) Add a way to reveal all keyboard shortcuts directly in the app - so you don't have to go to https://docs.webstudio.is/university/foundations/shortcuts every time 🙂
E) Perhaps add [+] as an alternative to "Add component" which is currently [A]