Output, scrolling, collapsed and UI

[marking as 5.0]

I find the "toggle" output/toggle scroll UI confusing, especially with multiple selection.
if I have 1 cell collapsed, 1 cell not collapsed and both selected I do not want to "toggle". Even with 1 cell, I do not want to toggle.

Proposal change the
- Toggle
- Toggle scrolled

To the following:
- Expand
- Scroll
- Collapse

It has the nice advantage of being stateless with respect to the current state of the notebook, and we can still have a "smart" toggle that: (collapsed->scrolled->expanded), other direction, or cycle.

Could apply to **input** as well.

@ellisonbg, @fperez ?

Start by locating the notebook output controls described in the issue and review how selection, collapsed state, and scrolled state are handled. The work is done when separate Expand, Scroll, and Collapse actions behave predictably for multiple selected cells, with any corresponding input behavior addressed.

Written by the indexing model from the issue text.