Jupyter: tweak cell prompt and buttonbar

[haraldschilly]

Description

1. removing the hover menu of the prompt
2. removing the copy/paste button from button bar
3. adding the above in a "more" menu in the buttonbar
   • it's a collection of copy/cut/paste operations, explaining when it is about the cell and when about the content
   • also merging and split at cursor
   • undo/redo
4. styling: the "current cell" box now goes around the cell, which needed several css tweaks.
   • this also enables showing the edit buttons for the markdown cells, without overlapping with the content
   • all cells now also show the running number, regardless if they're empty or not

"more" dropdown menu

this shows the active cell + numbering

current cell box when cell edit menu for nbgrader is active

Checklist:

• [ ] Testing instructions are provided, if not obvious
• [ ] Release instructions are provided, if not obvious

[williamstein]

removing the hover menu of the prompt

Yeah!

I don't dislike this

However, in a bazillion places all over, I've been using the vertical ellipsis for the menu, in the same way that Chrome uses it:

For consistency, why not do that for the cell? Chrome is by far the most popular web browser and people are able to figure out the ... menu thing there, so it seems likely people will be able to figure out that this is the menu. It's simple, clean and consistent.

Even here in Github it is similar (but horizontal):

[haraldschilly]

yes, sure, I changed the icon and well, after a bit of refactoring it should be fine to merge.

let's see if there are build errors – otherwise it is good to go.

[williamstein]

otherwise it is good to go.

Nice!!