Add "top artists" chart

android/gradle.properties

assets/translations/en.json

assets/translations/fr.json

fastlane/metadata/android/en-US/changelogs/25.txt

fastlane/metadata/android/fr-FR/changelogs/25.txt

lib/models/topartists.dart

lib/network/scrobbles_api.dart

lib/ui/screens/home_screen.dart

lib/ui/widgets/main_screen/topartists_card.dart

lib/ui/widgets/main_screen/topartists_chart.dart

lib/ui/widgets/main_screen/topartists_content.dart

pubspec.yaml