Add analytics on EMS registrations from server selector screen

**Is your feature request related to a problem? Please describe.**
The "Select a server" screen is very confusing for new users.
I don't think much users subscribe to EMS by hearing about it from that screen. Average users won't pay, when there are free alternatives. It's only confusing for them. Even if a large company or organisation subscribes to EMS, the employees or members don't have to know that it's an EMS hosting (e.g. Mozilla members enter mozilla.org as HS, not mozilla.modular.im), so only the admins need to know it.
EMS subscribers, which are mostly organisations or companies probably find it on element.io, instead of from the app. When an organisation looks for premium hosting, they rather open the webpage of the provider instead of downloading an app and trying if they find anything about premium hosting in the app.

**Describe the solution you'd like**
Add analytics on EMS registration from server selector screen.
If it is low, the button should be switched with the "Custom server" button (so it would be the 3rd instead of 2nd), or removed.