tremotesf2

Store file/directory data in TorrentFilesModelEntry in std::variant instead of using polymorphism, and remove synthetic root directory in BaseTorrentFilesModel

Simplify getting file ids from model indexes

Calculate directory properties only when they change and store them, and remove changed flag from TorrentFilesModelFile

Fix dataChanged signal not being emitted when files' priority is changed from UI

Add TorrentFilesModelTest