Collapse sub-notes

[eagerm]

I'd like to be able to collapse all notes under a parent note.

For example, if I have a book with ten chapters each of which has ten section, there would be 100 lines in the outline which makes it difficult to find notes in later chapters.

[djsudduth]

I would also like to see this - large hierarchical lists are hard to navigate

[dvorka]

@eagerm @djsudduth thanks - will give this higher priority!

[dvorka]

Related to #1380 and #1086