[BT] Refactored common TorrentFilesModel into Base.
[BT] Moved MkParentIfDoesntExist() to Base.
[BT] Split TorrentFilesModel.

Moved AddTorrent-only relevant stuff into AddTorrentFilesModel.
[BT] Fixed spinbox range in torrent tab Files pane.
[BT] Fixed TorrentFilesModelBase::rowCount().

Return proper row count for all columns.
[BT] Allow editing paths and priorities for non-leafs.
[BT] Removed unused function.
[BT] Recursive priorities setting in TorrentFilesModel.