Originally, it was just a wrapper for libtorrent::torrent_handle class, so it mimicked its name.
It was then transformed into a more complex aggregate, but the name was retained (just by inertia).
Unlike libtorrent::torrent_handle class in whose name "handle" means the pattern used,
it does not matter for qBittorrent classes and just eats up space in the source code.
Model returns string for DisplayRole.
Text alignment is set by Model (using TextAlignmentRole).
Delegate performs custom painting only where necessary
(i.e. for Progress bar).
Previously lookup is O(n), add operation is O(n), remove operation is
O(n).
Now lookup is O(1), add operation is O(1), remove operation is O(n).
n is the number of torrents already recorded.
