Let the user minimize the LTN left panel for all screens.

[dabreegster]

Implement in a pretty verbose way, just to get it working.

https://user-images.githubusercontent.com/1664407/169329109-d7982b3c-bec6-405d-bd35-60b656da2bfb.mp4

@dingaaling, this is not quite what you described. I'm not sure how to fit the left arrow on the top-right corner of the panel in all cases, without forcing the entire left panel to be slightly wider. Maybe the minimize arrow should go inside the "Policy proposals" box? That's semantically weird; that's meant to be the section of the panel for loading/saving/switching proposals.

Also, it's a bit useless to hide the panel in some of the modes. Like for route planning, you can't start a new route without showing the panel again. Should hotkeys of hidden panel buttons still work? Should we only have a minimize/maximize button in the two "edit neighborhood" modes?

[dingaaling]

I see what you mean - for many of the use cases you need the panel. I think it's still nice to have the option to minimize it though! I feel for initial exploration & visual demo it's nice to have it minimized.

[dabreegster]

I feel for initial exploration & visual demo it's nice to have it minimized.

Yeah totally, I think we need this feature, I'm just not sure how it should work.

1. Should it only be there for some modes?
2. If you hide the panel, change mode, should it stay hidden or reset?
3. If the user remembers keybindings, should they work while the panel is hidden?

[dabreegster]

New panel changes do this way better