Improve images resizing quality accross the board

- Using mipmap: true and smooth: true for images that are downscaled
(avatar, icons, ...)
- Using mipmap: false and smooth: true for images that are potentially
upscaled (background, overview, ...)

Widgets/Sidebar/Config/ProfileSettings.qml

@@ -70,8 +70,8 @@ Rectangle {
                         visible: false
                         asynchronous: true
                         cache: false
-                        sourceSize.width: 64
-                        sourceSize.height: 64
+                        smooth: true
+                        mipmap: true
                     }
                     
                     OpacityMask {