for some usages, specially with autostart enabled, user might want to
launch only the systray.

this commit implements a simple ``--nowindow`` switch that just avoids
showing the main window for now. in the future, we can have a different
entrypoint that just launches bitmaskd and a minimal systray widget.

I'm not documenting this feature properly since I think this is still
missing some functionality: the ability to switch on and off the vpn,
and the ability to pass the --autostart as a flag to the bitmask
entrypoint.

for now, we'll be hardcoding tcp as a more reliable alternative, no
matter what the provider announces.

explicitely specifying ipv4 should fix the case in which vpn fails to
start because ipv6 is disabled.

-Resolves: #9181, #9129

honor the anonymous certificate for the providers that offer it.
this still needs a change in bonafide, in which if provider supports
anonymous access we still have to download eip-service.json

for testing, I assume this has been already manually downloaded.