FXVPN-337 Return of the loading screen

[strseb]

If you look closely on the Screen Recording Shared with QA, you see the Red dot on the Icon not appearing for quite a while.
This indicates firefox takes it's time inizializing the background script.

You can easily replicate that by dropping await new Promise((r) => setTimeout(r, Math.round(Math.random() * 5000))); somewhere in main::init().

Currently if we open the message port before the background script is done inizializing we are screaming into the void.
Sooo, let's allow ipc.js to close and re-open ports if there is noone answering on the other side.

For that ofc we need to show "Something" so i'm bringing back the loading screen we added and then removed. 🙈

Here is a demo with a random delay.

[strseb]

Note This is a hardcoded string. This is not a view people should see, so i chose that.
Otherwise should we use "Mozilla VPN" ? or just empty?

[strseb]

I'm using a grid to stack things, so the size is inherited from the child elements, (in contrast to pos-absolute stacking).

Also if we don't stack, we might show a blip with both at the same time on top of each other which is more noticable then when we stack them,.