Pluginify BTCPayNetworkProvider

[NicolasDorier]

Summary

1. This PR makes it possible for plugin to inject BTCPayNetwork.
2. It also decouple the transaction link generation responsability out of BTCPayNetwork.
3. Make it possible for plugins to override the configuration settings --chains by using SelectedChain.Add.
4. Introduce PluginServiceCollection, a concrete type of IServiceCollection injected into plugins. This allow notably to get so called BootstrapServiceProvider which expose some services even before startup.
5. --chains have a new settings *, which mean allow all the networks to be injected.
6. End of support for dead altcoins
7. Small refactor for the creation of the payment request viewmodel, we had some duplicated code

Decoupling of transaction link generation

This PR extract the transaction link generation out of the BTCPayNetwork class as an effort to break up dependencies to it.
Many more PR will need to follow to decouple the responsability of the "god class".

End of support for altcoins

Due to the heavy refactoring needed to support altcoins, I decided to remove alt those who are considered dead (no volume on exchange and more than top 1000).

• Althash
• Argoneum
• Bitcoin Plus
• Bitcore
• Feathercoin
• Polis
• UFO
• Viacoin

Those still interested in those coins will be able to pluginify them by themselves thanks to this PR.