[Enhancement] Back option in servers list

[zautumnz]

Is your feature request related to a problem? Please describe.
I frequently accidentally choose the wrong country, for example if I meant to go into the server list for Ireland but accidentally hit enter on Israel. It would like to return to the list of countries without having to cancel and then run the program again.

Describe the solution you'd like
An option in the list to go back to the countries list

Describe alternatives you've considered
The only alternative right now is hitting cancel, then re-running protonvpn c

Additional context
I have a change ready to submit as a PR if this feature would be welcome. This is not related to #153, my change is in the dialog menu.

[zautumnz]

Closing since I see in another PR that you're working on a complete rewrite.