use a provider selector
As part of the customization, we need to let the user choose what is their provider of choice. (#315 for UI proposals).
One possible implementation is to define all the libraryVPN providers in the pre-seeded providers.json (#326 (closed)), and use a provider selection dialog as par of the first-run (with a dropdown for the time being).
We could also make the client "forget" the provider (we'd need a "log me out" option in the systray menu for this).