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.
In addition to the current tooltip, which shows color legend, if user
holds the Shift key during hovering we show another tooltip which
contains a table of contents for the piece under the moue cursor. The
table lists file sizes and names. If the cursor points to a part of a
file which spans several pieces, those pieces are highlighted.
