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

rtdata/images/svg/index.theme

@@ -0,0 +1,55 @@
+[Icon Theme]
+Name=RawTherapee
+Comment=RawTherapee icon theme
+Inherits=Adwaita
+Directories=16x16/app_icons,24x24/app_icons,32x32/app_icons,48x48/app_icons,64x64/app_icons,128x128/app_icons,256x256/app_icons,scalable/app_icons,scalable/apps
+
+
+[16x16/app_icons]
+Size=16
+Context=ApplicationIcons
+Type=Threshold
+
+[24x24/app_icons]
+Size=24
+Context=ApplicationIcons
+Type=Threshold
+
+[32x32/app_icons]
+Size=32
+Context=ApplicationIcons
+Type=Threshold
+
+[48x48/app_icons]
+Size=48
+Context=ApplicationIcons
+Type=Threshold
+
+[64x64/app_icons]
+Size=64
+Context=ApplicationIcons
+Type=Threshold
+
+[128x128/app_icons]
+Size=128
+Context=ApplicationIcons
+Type=Threshold
+
+[256x256/app_icons]
+Size=256
+Context=ApplicationIcons
+Type=Threshold
+
+[scalable/app_icons]
+MinSize=16
+Size=128
+MaxSize=256
+Context=ApplicationIcons
+Type=Scalable
+
+[scalable/apps]
+MinSize=16
+Size=128
+MaxSize=256
+Context=Applications
+Type=Scalable