Use checkable action for alternative speed limits and display button as "pressed when enabled"

src/GUI.cpp

@@ -947,13 +947,7 @@ void GUI::createSystrayDelayed() {
 }
 
 void GUI::updateAltSpeedsBtn(bool alternative) {
-  if(alternative) {
+    actionUse_alternative_speed_limits->setChecked(alternative);
-    actionUse_alternative_speed_limits->setIcon(QIcon(":/Icons/slow.png"));
-    actionUse_alternative_speed_limits->setText(tr("Use normal speed limits"));
-  } else {
-    actionUse_alternative_speed_limits->setIcon(QIcon(":/Icons/slow_off.png"));
-    actionUse_alternative_speed_limits->setText(tr("Use alternative speed limits"));
-  }
 }
 
 QMenu* GUI::getTrayIconMenu() {
@@ -965,6 +959,7 @@ QMenu* GUI::getTrayIconMenu() {
   myTrayIconMenu->addAction(actionDownload_from_URL);
   myTrayIconMenu->addSeparator();
   updateAltSpeedsBtn(Preferences::isAltBandwidthEnabled());
+  actionUse_alternative_speed_limits->setChecked(Preferences::isAltBandwidthEnabled());
   myTrayIconMenu->addAction(actionUse_alternative_speed_limits);
   myTrayIconMenu->addAction(actionSet_global_download_limit);
   myTrayIconMenu->addAction(actionSet_global_upload_limit);

src/statusbar.h

@@ -195,6 +195,7 @@ public slots:
     if(alternative) {
       altSpeedsBtn->setIcon(QIcon(":/Icons/slow.png"));
       altSpeedsBtn->setToolTip(tr("Click to disable alternative speed limits"));
+      altSpeedsBtn->setDown(true);
     } else {
       altSpeedsBtn->setIcon(QIcon(":/Icons/slow_off.png"));
       altSpeedsBtn->setToolTip(tr("Click to enable alternative speed limits"));

src/ui/mainwindow.ui

@@ -269,12 +269,14 @@
    </property>
   </action>
   <action name="actionUse_alternative_speed_limits">
-   <property name="icon">
+   <property name="checkable">
-    <iconset resource="../icons.qrc">
+    <bool>true</bool>
-     <normaloff>:/Icons/slow_off.png</normaloff>:/Icons/slow_off.png</iconset>
    </property>
    <property name="text">
-    <string>Use alternative speed limits</string>
+    <string>Alternative speed limits</string>
+   </property>
+   <property name="toolTip">
+    <string>Alternative speed limits</string>
    </property>
   </action>
   <action name="actionTop_tool_bar">