Follow up to PSR-4 migration: App.php to application migration

[burned42]

I noticed that one of the files I moved in #222 was the app.php which contains the class Application. I took a look at the documentation at https://docs.nextcloud.com/server/latest/developer_manual/app_development/bootstrap.html which says that the app.php is deprecated and I think the code inside should be adjusted as well.

I used said documentation and also took a look at different applications under https://github.com/nextcloud e.g.

• register event listener: https://github.com/nextcloud/server/blob/81bb3362b24a621fb399877739e7bff35ec13eb7/apps/systemtags/lib/AppInfo/Application.php#LL49C1-L49C1
• navigation entry:
  • https://docs.nextcloud.com/server/latest/developer_manual/app_development/info.html
  • https://github.com/nextcloud/contacts/blob/main/appinfo/info.xml#L53

I deactivated and removed keeweb from my instance, built keeweb as described in README, uploaded, extracted and activated it and it still works for me and I don't get any log entries on debug loglevel.

Related to #219 (works for me without issues, so this time the issue might be resolved for real)