WIP: Eventually consistent multiplayer 🤝

[Pangoraw]

Still very wip. Different take at #1729.

TODO:

• Entering Unicode characters
• Evaluates the size of updates array after a while and maybe drop old
  updates.
• Playing nice with FileWatching (is it possible?)
• The client is not always synced when sending run_multiple_cells
  -a cell [ ] Global state manager
• Rebasing updates on the server to not refuse client updates.
• Make running a cell as simple as dispatching a Run effect, this means that
  we can get the history up until a run. Also this is a similar mechanism to Add run_requested_timestamp state to delete the run_multiple_cells action #2542 where we can merge run updates.
  last_schedule_time will just a be a revision in the codemirror update history.
• Send JuliaSyntax.jl diagnostics as transaction effects from the server.
• Investigate using Deltas in the backend instead of manipulating codemirror update types.
• Add possibility to select/change name and show other people's name
• Rework code differs since it now relies on the server synced version (use cell local state instead).
• Save last_run_code instead of code? Solution: save the code as cell metadata if they are not the same and when loading take this into account.

Cursor stuff:

• Don't show your own cursor.
• Only show focused cursor.
• Integrate with
  f3fce3e
  for client disconnects (hiding cursors), etc...
• Register pinot

See
Pinot.jl.

[github-actions]

Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/fonsp/Pluto.jl", rev="pb/ot")
julia> using Pluto

[gdalle]

Hey there! Small question: how can I decide to run this branch of Pluto on Binder?