Improve UX when the user is not logged in

[PWrzesinski]

When running XcodesApp for the first time, it took me a while to figure out that I need to log in before I can download Xcode - it was a while ago, but the error was quite unclear at the time (see #164 and #165). This has been fixed since, but I hope making the button red when the user is not authenticated will improve the UX a little bit, guiding the user to click it.

It's a minor improvement that was at the back of my mind ever since that first time and I finally got around to implementing it. Please let me know if this kind of UI change is welcome or not.

[MattKiazyk]

Hey @PWrzesinski Thanks for taking the time for this PR!

Couple of thoughts:

• I agree that there should be something to notify the user they need to log in, I don't mind the red, but I'm almost wondering if words should also appear on next to the button - similar to how filters work:

- Secondly - that `authenticationState` needs some work as by default when you first open the app, it doesn't even check it, so it will always be red when you first open up the app, and only show what it actually is after it's refreshed. So I think there's some improvement there that needs to happen at the same time for the red icon on the main list to be useful.

Let me know if you have any questions.

[PWrzesinski]

Thanks for taking a look @MattKiazyk! I've updated the implementation. Here's how it looks currently:

• At the start:

• When not logged in:

Considering if the red color is needed now, or perhaps the default one will do nice. I've added the check for authentication state in the AppState init, is that ok? Completely new to this code base.

I couldn't fully test the new functionality as it seems I'm logged out every time I start the app, probably denied it access to the keychain or something.

Also got a couple of general questions:

• How do I go about localizing the new copy?
• In Contributing.md there is a mention of linting, but I can't find any configuration in the project - ok to ignore, or should I just run Swiftlint with a default config?
• Didn't add any tests for the changes, doesn't feel necessary here.