App setup should have a step allowing connection to own Electrum Server before vault creation

[ben-kaufman]

On first open, we should let the user explicitly choose between connecting to own electrum, or use a public one, instead of using public by default without asking. This is needed so when creating the first hot wallet, it will avoid doing any query that may expose addresses to a public server.

We should still make sure to keep it very easy for users to simply continue with public server, to avoid making setup confusing for beginners.