Standardize deletion and removal confirmations

[sdaitzman]

When deleting a library object, we want to make sure users understand that it will be:

• Removed from other library objects it was previously part of, if any (Delete component that's used in a unit #1685)
• Unlinked from local objects used in courses

Spec

• When a library object that has already been used in a course is deleted in a library, the warning that course objects will be unlinked should be included
  • The warning can link to the specific course, or list multiple courses
• When a library object not used in a course is deleted, the warning should be omitted.

Rough mockup (copy to be adjusted)

UX/UI tasks

• Generate spec/mockups of confirmation dialog conditional on: course reuse, library reuse, library object level
• Edit copy

[sdaitzman]

(Placed under #1645 because the intent is to consolidate library object deletion warnings across all object types to prevent section- and subsection-level authoring dialogs from becoming extremely unwieldy)