Added MVVM choice for F# MVVM template

[Mrxx99]

This adds the same choice for MVVM framework that the C# MVVM template has to F#.
Fixes #108

[Mrxx99]

@Takoooooo Is there a specific reason why ReactiveUi uses a additonal ViewModelBase class and CommunityToolkit does not? It would simplify the templates if this would be uniform.

[Takoooooo]

@Takoooooo Is there a specific reason why ReactiveUi uses a additonal ViewModelBase class and CommunityToolkit does not? It would simplify the templates if this would be uniform.

Makes sense,probably. I will merge this PR and we can do that in the separate one

[Mrxx99]

Makes sense,probably. I will merge this PR and we can do that in the separate one

Ok, to what should we uniform? That ViewModelBase is used for all or that it is not used at all?

[Takoooooo]

Makes sense,probably. I will merge this PR and we can do that in the separate one

Ok, to what should we uniform? That ViewModelBase is used for all or that it is not used at all?

Let's leave ViewModelBase for both

[Takoooooo]

LGTM,thanks! Also at this point i assume we may close this issue as fixed.