Initial commit for real hidpi support

Note: This commit has only been tested on MacOS

Changes:
- Icons now use the native hidpi support from Gtk (through Icon Theme)
- Icons are now directly generated from scalable file (i.e. SVG file)
- Widget sizes are scaled based on DPI and scale factor
- Font size is scaled based on DPI and scale factor

rtgui/editwindow.h

@@ -31,7 +31,6 @@ class EditWindow :
 {
 
 private:
-    double resolution;
     RTWindow* parent;
     RTImage appIcon;
 
@@ -44,8 +43,6 @@ private:
     bool isMinimized;
     sigc::connection onConfEventConn;
     void toggleFullscreen ();
-    bool updateResolution();
-    void setAppIcon();
 
     IdleRegister idle_register;