[Feature request] Handle staves with any number of staff lines

Now that we're exploring many different manuscripts, we'll be creating MEI files that have staves with anywhere from 1 to 5 staff lines, maybe even more. I believe that Neon only supports four-line staves at the moment, so it'll have to be expanded.

A request for five-line staves has already been made [here](https://github.com/DDMAL/Neon/issues/1358), and a bug with the one-line staff has been reported [here](https://github.com/DDMAL/Neon/issues/1313); I'll close those issues, because this larger request should fix all of that.

There are a few sub-issues I can think of (I'll make them as actual sub-issues as well):

- [ ] Enable Neon to support staves with different numbers of lines within a single folio.
- [ ] Allow the user to edit the number of lines a staff has; this can appear as an option in the Edit panel when a user selects a staff.
- [ ] Allow a user to select the number of lines they want in a staff they're updating; the Insert panel for staves could be updated to include staves with 1 to 5 staff lines, plus a customizable option.

Start by tracing staff handling in the Edit and Insert panels and how the editor represents MEI staves; the issue names no files or tests. Done means supporting staves with one to five or more lines, mixed line counts within one folio, and user selection or editing of each staff's line count.

Written by the indexing model from the issue text.