Improve "Watched folders" feature

Make "file system watcher" an application core component
and separate it from its presentation model.

src/base/base.pri

@@ -36,7 +36,6 @@ HEADERS += \
     $$PWD/bittorrent/trackerentry.h \
     $$PWD/digest32.h \
     $$PWD/exceptions.h \
-    $$PWD/filesystemwatcher.h \
     $$PWD/global.h \
     $$PWD/http/connection.h \
     $$PWD/http/httperror.h \
@@ -70,7 +69,6 @@ HEADERS += \
     $$PWD/rss/rss_item.h \
     $$PWD/rss/rss_parser.h \
     $$PWD/rss/rss_session.h \
-    $$PWD/scanfoldersmodel.h \
     $$PWD/search/searchdownloadhandler.h \
     $$PWD/search/searchhandler.h \
     $$PWD/search/searchpluginmanager.h \
@@ -78,6 +76,7 @@ HEADERS += \
     $$PWD/settingvalue.h \
     $$PWD/tagset.h \
     $$PWD/torrentfileguard.h \
+    $$PWD/torrentfileswatcher.h \
     $$PWD/torrentfilter.h \
     $$PWD/types.h \
     $$PWD/unicodestrings.h \
@@ -122,7 +121,6 @@ SOURCES += \
     $$PWD/bittorrent/tracker.cpp \
     $$PWD/bittorrent/trackerentry.cpp \
     $$PWD/exceptions.cpp \
-    $$PWD/filesystemwatcher.cpp \
     $$PWD/http/connection.cpp \
     $$PWD/http/httperror.cpp \
     $$PWD/http/requestparser.cpp \
@@ -151,13 +149,13 @@ SOURCES += \
     $$PWD/rss/rss_item.cpp \
     $$PWD/rss/rss_parser.cpp \
     $$PWD/rss/rss_session.cpp \
-    $$PWD/scanfoldersmodel.cpp \
     $$PWD/search/searchdownloadhandler.cpp \
     $$PWD/search/searchhandler.cpp \
     $$PWD/search/searchpluginmanager.cpp \
     $$PWD/settingsstorage.cpp \
     $$PWD/tagset.cpp \
     $$PWD/torrentfileguard.cpp \
+    $$PWD/torrentfileswatcher.cpp \
     $$PWD/torrentfilter.cpp \
     $$PWD/utils/bytearray.cpp \
     $$PWD/utils/compare.cpp \