Inhibit sleep regardless of activity

"Active torrents" is a somewhat unintuitive concept as a basis for
preventing sleep, as torrents can become active or inactive on the
network at any time. This brings some predictability to the inhibit
sleep option, and will inhibit sleep as long as there are unpaused
downloads or uploads, regardless of network activity.

Closes #1696, #4592, #4655, #7019, #7159, #7452

src/gui/mainwindow.h

@@ -173,8 +173,8 @@ private slots:
     void on_actionDownloadFromURL_triggered();
     void on_actionExit_triggered();
     void on_actionLock_triggered();
-    // Check for active torrents and set preventing from suspend state
-    void checkForActiveTorrents();
+    // Check for unpaused downloading or seeding torrents and prevent system suspend/sleep according to preferences
+    void updatePowerManagementState();
 #if defined(Q_OS_WIN) || defined(Q_OS_MAC)
     void checkProgramUpdate();
 #endif