Switch UI framework

[paoloambrosio]

• The current UI needs rewriting because it's in a terrible state (didn't know what I was doing). Should use modern techniques like ReactiveUI or MVVM Toolkit. A better example is the MEME prototype.
• Have to switch UI framework for a Linux build (see Linux support #96). Some options:
  • AvaloniaUI with third-party widgets including LiveCharts.
  • Electron.NET, Blazor and MudBlazor
• Some users are even running Windows 7 or 8.
• Implement localisation from the start.