- The function returns one of three values:
  1 - The user's preference (user.settings.preferences.<preference>)
  2 - The default system setting value (Default_User_Preferences_<preference>)
  3 - A default value passed as argument to the function

- Besides the introduction of the helper function:
  - Removes unused preferences (user.settings.preferences.unreadRoomsMode, user.settings.preferences.audioNotificationValue) and creates migration script (v105)
  - Implements some simple tests

[FIX] RTL on reply

[FIX] Only use "File Uploaded" prefix on files

attachments older than the current day

Closes #5934