Separate Expand and Collapse key bindings

Currently, Dynalist only has one action for toggling expand/collapse. Unfortunately, this has an important limitation: it makes it difficult to collapse to N parent levels.
- root
- level 1
- level 2a
- level 2b
- level 2c
- level 2d
- level 2e
- level 2e-a
- level 2e-b # <— cursor is here

If Dynalist had a separate “collapse” vs “expand” shortcut, collapsing up to level 1 would only take two keypresses ( + ). This is because Dynalist would be able to understand that the user wants to collapse the current item to the parent level.

With a single expand/collapse shortcut, Dynalist can’t guess whether the user wants to expand or collapse, so it has to act conservatively and do nothing.

To collapse the the parent, one has to do some gymnastics to navigate to the parent (multiple keypresses), do <expand/collapse>, then re-navigate to the grand-parent (again multiple keypresses) then do <expand/collapse> again.