Allow swiping away notifications without marking channel as read

...uschku/quasseldroid/service/QuasselNotificationBackend.kt

...in/java/de/kuschku/quasseldroid/service/QuasselService.kt

...u/quasseldroid/service/QuasseldroidNotificationManager.kt

.../de/kuschku/quasseldroid/settings/NotificationSettings.kt

...rc/main/java/de/kuschku/quasseldroid/settings/Settings.kt

app/src/main/res/values-de/strings_preferences.xml

app/src/main/res/values/strings_preferences.xml

app/src/main/res/xml/preferences.xml

...va/de/kuschku/quasseldroid/persistence/QuasselDatabase.kt