The svg2png icon cache is now cleared on new minor version

The `version` value from the `Options` file is compared to the harcoded
value (computed at build time) of the running application. If the major
or minor version is different, the `svg2png` folder is cleaned at
startup-time.

rtgui/rtimage.cc

@@ -169,7 +169,7 @@ void RTImage::init()
     scaleBack = RTScalable::getScale();
 }
 
-void RTImage::cleanup()
+void RTImage::cleanup(bool all)
 {
     for (auto& entry : pixbufCache) {
         entry.second.reset();
@@ -177,7 +177,7 @@ void RTImage::cleanup()
     for (auto& entry : surfaceCache) {
         entry.second.clear();
     }
-    RTScalable::cleanup();
+    RTScalable::cleanup(all);
 }
 
 void RTImage::updateImages()