Fix transparency of speed limits icons

Dropped dependency on Qt gif library

src/icons.qrc

@@ -6,12 +6,12 @@
   <file>Icons/url.png</file>
   <file>Icons/locale.png</file>
   <file>Icons/loading.png</file>
-  <file>Icons/slow_off.gif</file>
+  <file>Icons/slow.png</file>
   <file>Icons/magnet.png</file>
   <file>Icons/sphere.png</file>
+  <file>Icons/slow_off.png</file>
   <file>Icons/uparrow.png</file>
   <file>Icons/rss16.png</file>
-  <file>Icons/slow.gif</file>
   <file>Icons/skin/checkingUP.png</file>
   <file>Icons/skin/bg-handle-horizontal.gif</file>
   <file>Icons/skin/play.png</file>

src/statusbar.h

@@ -190,10 +190,10 @@ public slots:
 
   void updateAltSpeedsBtn(bool alternative) {
     if(alternative) {
-      altSpeedsBtn->setIcon(QIcon(":/Icons/slow.gif"));
+      altSpeedsBtn->setIcon(QIcon(":/Icons/slow.png"));
       altSpeedsBtn->setToolTip(tr("Click to disable alternative speed limits"));
     } else {
-      altSpeedsBtn->setIcon(QIcon(":/Icons/slow_off.gif"));
+      altSpeedsBtn->setIcon(QIcon(":/Icons/slow_off.png"));
       altSpeedsBtn->setToolTip(tr("Click to enable alternative speed limits"));
     }
   }

src/ui/options.ui

@@ -1478,6 +1478,16 @@ QGroupBox {
                    </item>
                   </layout>
                  </item>
+                 <item>
+                  <widget class="QLabel" name="label_5">
+                   <property name="text">
+                    <string notr="true"/>
+                   </property>
+                   <property name="pixmap">
+                    <pixmap resource="../icons.qrc">:/Icons/slow_off.png</pixmap>
+                   </property>
+                  </widget>
+                 </item>
                  <item>
                   <spacer>
                    <property name="orientation">
@@ -1588,7 +1598,7 @@ QGroupBox {
                     <string/>
                    </property>
                    <property name="pixmap">
-                    <pixmap resource="../icons.qrc">:/Icons/slow.gif</pixmap>
+                    <pixmap resource="../icons.qrc">:/Icons/slow.png</pixmap>
                    </property>
                    <property name="scaledContents">
                     <bool>false</bool>