GUI: Show ideal thread count next to current thread count.

Ideal thread count is determined by Qt as number of available cores.
Ticket: #2194 (Automatically match thread count to available cores)

gui/settings.ui

@@ -103,6 +103,20 @@
            </property>
           </widget>
          </item>
+         <item>
+          <widget class="QLabel" name="label_3">
+           <property name="text">
+            <string>Ideal count:</string>
+           </property>
+          </widget>
+         </item>
+         <item>
+          <widget class="QLabel" name="mLblIdealThreads">
+           <property name="text">
+            <string>TextLabel</string>
+           </property>
+          </widget>
+         </item>
          <item>
           <spacer name="horizontalSpacer">
            <property name="orientation">

gui/settingsdialog.cpp

@@ -26,6 +26,7 @@
 #include <QTabWidget>
 #include <QSettings>
 #include <QFileDialog>
+#include <QThread>
 #include "settingsdialog.h"
 #include "applicationdialog.h"
 #include "applicationlist.h"
@@ -70,6 +71,12 @@ SettingsDialog::SettingsDialog(QSettings *programSettings,
     mUI.mListWidget->setSortingEnabled(false);
     PopulateListWidget();
 
+    const int count = QThread::idealThreadCount();
+    if (count != -1)
+        mUI.mLblIdealThreads->setText(QString::number(count));
+    else
+        mUI.mLblIdealThreads->setText(tr("N/A"));
+
     LoadSettings();
 }