Added demo image for resolution independence
Code formatting
[BUG #7762] Review px-based mobile code and make it resolution-independent
* Added a method to qx.Mobile root to adjust application's scale factor
* Updated qx.Mobile image to use a higher resolutions image based on device pixel ratio and application's scale factor.
[BUG #7762] Review px-based mobile code and make it resolution-independent
* Added an example for showcasing the image resolution handling, based on device pixel ratio and application's scale factor