Course outline: Add sidebar updates

[navinkarkera]

Adding a few more details here on detailed scenarios. I edited my comment above to remove open questions:

• Because content cannot be added to library referenced object, the selected content should add to the last possible location (ie: if adding a subsection but the last section is a library referenced section, add to the section above).
• If there is no possible place to add content (ie: empty state, only library content exists) new content should be created. For example, if a user clicks to add new unit to a blank course, a section, subsection, should be added in addition to the unit.

Originally posted by @edschema in #2629

Hi @bradenmacdonald @navinkarkera
For sidebar responsiveness, there are still some things to finish but wanted to share here:

• instead of a max sidebar size, I think we should define a minimum outline size.
• Sidebars should be responsive and resizable. There should be a minimum sidebar width as well, To be defined.
• filter and sort should be responsive:

Originally posted by @edschema in #2778 (comment)

Hi @navinkarkera @ChrisChV some more detail on the add sidebar:

• If a library block is selected, user cannot add content to it. The sidebar should display this notification. This notification should appear for both new and existing tabs.

• If a subsection is added (or a section is selected and add sidebar opened), whether added content is new or existing dictates the behavior:
  • for any new content, info sidebar should be opened for the newly created object. ie: subsection is added, the subsection should be selected with the info tab open
  • For new units added from the course outline page, user should be navigated to the unit page for the new component with the info sidebar open
  • for added existing content, the viewport should scroll to have the added content in view, but the sidebar should remain with the correct context in the add flow. This is because we suspect authors adding existing content are building from a library and will want to continue adding content.
  • If a unit is selected on the course outline page, and a user clicks the add sidebar, the add sidebar for units should render. If a user adds existing, the unit page should be opened with the added component in view, but the unit page add sidebar open
  • I user adds new content to a unit from the outline page, the unit page should open with the newly created content's add modal open.
• On the headers: the sidebar headers should still have the back button for add sidebars.

Originally posted by @edschema in #2631