Switch app ID to those of the main app

[gnprice]

As part of launching this app as the new Zulip mobile app (cf #715), we'll need to switch the app ID it uses to the app IDs we use for the main Zulip listings in the Play Store and App Store respectively.

Those are com.zulipmobile on Android and org.zulip.Zulip on iOS. To date, this app has been using com.zulip.flutter.

(The values we'll switch to are a bit funny-looking, yes. This is an aspect that's completely invisible to users, and very costly to change once an app is published, so early legacy values persist forever.)

Implementation

In addition to being the app ID on all platforms, "com.zulip.flutter" is also the JVM "package" name of our Kotlin code. I believe we can leave that unchanged, and that changing it would be somewhat more complex, so let's try to leave that unchanged. In particular I think this means that in android/app/build.gradle we'll change applicationId to be "com.zulipmobile", but leave namespace as "com.zulip.flutter".

The name "com.zulip.flutter" is also the app ID of the Linux and macOS apps, and I don't see a reason to change those.

In general, run git grep com.zulip.flutter and look at each of the results. Many of those instances will change, and some won't.

References

• Related previous issue (was a prerequisite for this one): notif: Use live value for app ID on registering APNs token #407