Fable.Elmish 4.0 support

[mrakgr]

PS E:\Webdev\Fable\CFR-In-Fable\src\Server> paket add Fable.SignalR.Elmish
Paket version 7.2.1+8e4eb74b42fbd45f39f7afce9184c16ebb65f16c
Adding package 'Fable.SignalR.Elmish'
Resolving dependency graph...
  Conflict detected:
   - Fable.SignalR.Elmish 0.11.5 requested package Fable.Elmish: >= 3.1 < 4.0
   - Elmish.Bridge.Client 7.0.2 requested package Fable.Elmish: >= 4.0
   - Fable.Elmish.React 4.0 requested package Fable.Elmish: >= 4.0

At this point the library is out of date and needs upgrading.

    Fable.FastCheck (0.33)
      Fable.Core (>= 3.2.8 < 4.0)
      Fable.Elmish (>= 3.1 < 4.0)
      Fable.Promise (>= 2.2.2 < 3.0)
      FSharp.Core (>= 4.7.2)

In particular the library that is blocking us here is this one. Since FastCheck is just for testing, would it be possible to omit it?

[ArtemyB]

@mrakgr I have a fork of the repo with some updates and fixes, that I'm currently using in my project alongside with Feliz 2+ and Elmish 4+. I haven't tested it thoroughly, but for now it seems working fine in my pretty simple scenario (although it includes streaming). However if you encounter any problems just create an issue so I could know what to fix 🙂

P.S. @Shmew is not active for a long time and does not respond to any issues, PRs, etc. in all of his repos.