View all orphan notebooks to aid categorisation into collections

[stuwilmur]

Is your feature request related to a problem? Please describe.
I like to keep my notebooks arranged in collections; ideally, I like to have every notebook in a parent collection, with no orphan notebooks that don't belong in a collection. However, I cannot find an easy way of viewing all my orphan notebooks in order to go through them and add each to a collection. What I currently have to do is trawl all my notebooks, and check each is already present in a collection.

Describe the solution you'd like
Some ideas include:

• on the list/grid of all notebooks, have some indication against each notebook that is already present in at least one collection, e.g. a collection icon next to it or similar.
• allow the user to see a view/grid/list of all orphan notebooks
• from the collections view, show the list of collections as normal, but also show all orphan notebooks - I think of this somewhat analogously to a GUI directory system where I have a bunch of "messy" files in the topmost directory, that have not yet been added to appropriate subdirectories.

Describe alternatives you've considered
None.

Additional context
None.

[mootari]

My preferred solution would be to make our search work with a negative collections filter like -collection: that excludes any notebook which is part of a collection. You can then combine this filter with any other like owner: to find unassigned notebooks in your own account.