Don't show the welcome window when opening from URL scheme or CLI command

[wvteijlingen-npo]

Current behavior
When Differati is opened using the URL scheme or CLI command, it not only shows the comparison indicated in the URL, but also shows the welcome window on top.

This is a bit annoying, because you first have to close the welcome window before you can see the actual comparison that you were looking for.

Desired behavior

1. Don't open the welcome window when Differati is launched using the URL scheme or the CLI command.
2. Additionally: if the welcome window is already visible, close it when Differati is brought to the foreground using the URL scheme or the CLI command.

[lkuczborski]

Wanted to take a minute appreciate the project, it is super useful and handy when comparing snapshot images. Thank You! 👏

Adding to @wvteijlingen-npo comment above, I noticed that it always opens a new Welcome window each time you trigger the app with URL scheme. So if previous one is not closed it will still spawn another one. This way you can end up with multiple Welcome windows if you are not closing it each time manually.