feat(notes): create a note from the List Notes search

[dionmunk]

Typing a name in Notes: List Notes (Alt+L) that wasn't a note left an empty list where Enter did nothing (#34).

Changes

• Create from the list. When the typed text isn't a note's name, a Create '<name>' entry is added at the end of the list. If nothing else matches it's the only entry, so Enter creates and opens the note. If something matches, Enter still opens the top match. With Workspace Notes there's one Create entry per section. No Create entry is offered when a note already has the typed name (with or without its extension).
• Notes in folders are listed. Before, only the top level of each location was listed. Notes in folders now show with their folder next to the name (and their section when there are two), and the folder can be searched too. Hidden files are left out, and files whose extension isn't allowed are left out like in the tree.
• One way to create a note. New Note and List Notes both use createNote, so both keep a typed extension (feat(notes): keep an extension typed with a new note's name #96) and only give Markdown notes a heading. It writes with the exclusive flag, so an existing file is never overwritten.

Testing

• npm test: 30 passing, 1 new test for matching a typed name to a note.

• End to end in VS Code 1.140 on macOS, with animals.md, ideas.txt, sub/more.md and a hidden .hidden.md:

  Scenario	master	this branch
  open the list	animals.md, ideas.txt	animals.md, ideas.txt, more.md (sub)
  type brand new idea, Enter	empty list, nothing happens	note created with # brand new idea and opened
  type anim, Enter		animals.md opens, Create entry last, no file created
  type animals		only animals.md, no Create entry
  type mo		more.md first, Create entry last
  type query.sql, Enter		query.sql created, empty
  with Workspace Notes, type kickoff		Create in Workspace Notes / in Notes; choosing Workspace Notes creates .notes/kickoff.md
  type, then Escape		nothing created

• New Note from both sections, the "where should it go" question, New Note with a note selected, and the typed extension rules from feat(notes): keep an extension typed with a new note's name #96 were re-run with the same results.

Closes #34.