Add option to automatically remove .torrent files upon adding

Some browsers do not download files, intended for immediate opening,
into a temporary directory, and thus a regular download directories
accumulate those unneeded files.

The option allows qBittorrent to clean after itself and delete those
files whether they were succesfully added or not (user-selectable
policy).

src/base/CMakeLists.txt

@@ -52,6 +52,7 @@ qinisettings.h
 scanfoldersmodel.h
 searchengine.h
 settingsstorage.h
+torrentfileguard.h
 torrentfilter.h
 tristatebool.h
 types.h
@@ -107,6 +108,7 @@ preferences.cpp
 scanfoldersmodel.cpp
 searchengine.cpp
 settingsstorage.cpp
+torrentfileguard.cpp
 torrentfilter.cpp
 tristatebool.cpp
 )