WebUI: make API locale independet

Sizes are now given in bytes.
Dates are Unix timestamps and converted to ISO 8601 in the web UI.
Numbers are not converted to strings.
-1 is returned for undefined values.

Some keys have been splitted:

Torrent list (json/torrents)
 * num_seeds: Torrent seeds connected to
 * num_complete: Torrent seeds in the swarm
 * num_leechs: Torrent leechers connected to
 * num_incomplete: Torrent leechers in the swarm

Torrent generic properties (propertiesGeneral/hash)
 * total_uploaded: Total data uploaded
 * total_uploaded_session: Total data uploaded this session
 * total_downloaded: Total data dowloaded
 * total_downloaded_session: Total data downloaded this session
 * time_elapsed: Torrent elapsed time
 * seeding_time: Torrent elapsed time while complete
 * nb_connections: Torrent connection count
 * nb_connections_limit: Torrent connection count limit

Global transfer info (json/transferInfo)
 * dl_info_speed: Global downalod rate
 * dl_info_data: Data downloaded this session
 * up_info_speed: Global upload rate
 * up_info_data: Data uploaded this session

Closes #1524.

src/qtlibtorrent/qtorrenthandle.cpp

@@ -103,6 +103,15 @@ QString QTorrentHandle::creation_date() const {
   return t ? misc::toQString(*t) : "";
 }
 
+qlonglong QTorrentHandle::creation_date_unix() const {
+#if LIBTORRENT_VERSION_NUM < 10000
+  boost::optional<time_t> t = torrent_handle::get_torrent_info().creation_date();
+#else
+  boost::optional<time_t> t = torrent_handle::torrent_file()->creation_date();
+#endif
+  return t ? *t : -1;
+}
+
 QString QTorrentHandle::current_tracker() const {
   return misc::toQString(status(0x0).current_tracker);
 }