Use Fluxor instead of ReactiveUI

[TolikPylypchuk]

Blazor doesn't seem to play nicely with MVVM, and ReactiveUI's support for Blazor is a little lacking. Also, there is no easy way to do application-wide state management (it was difficult even in the desktop app).

Fluxor (and the Redux pattern in general) seems to solve the state management problem, and will allow me to use Blazor more idiomatically, although I suspect it will be difficult to get used to this pattern compared to ReactiveUI.