Quickfix: No more double resizing of images

Fixes #856. Images are no longer double resized (e.g. on copy). 
Therefore they are no longer destroyed on copy (neat!).
Now it only resizes the image if both, the height and the width is bigger than the display of the device.

[Tests](https://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/1148/) are running, but I wasn't sure if I should write a test especially testing if double calling `copyImage` can destroy an image. How is this normally handled?

Also, I'm still not sure why the function `copyAndResizeImage` can destroy images. Maybe this could be refactored by someone with a little more time.