Changed the spinner to a non-GPL one, added instructions on how to regenerate it, changed the assets attribution, removed old spinner + old spinner's sources.

share/qt/how_to_generate_update_spinner.txt

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+How to generate the update_spinner.mng
+
+You will need ImageMagick in your path (the 'convert' executable at least)
+
+Go here: http://preloaders.net/en/circular
+
+Select the base image you want to use.
+
+Image type: APNG
+Transparent background: Yes
+Foreground color: F2A555 (or select a color)
+Animation speed: (default value)
+Preloader size: 16 x 16
+
+(no Advanced Options changed)
+
+Additional download options:
+
+Check Download as sprites
+
+Press Download now
+
+Rename the file to base.png
+
+convert -dispose 3 -delay 10 base.png -crop 16x16 +repage update_spinner.mng
+
+If you want to use the make_spinner.py (gives worse results):
+
+In http://preloaders.net/en/circular change
+
+Preloader size: 128 x 128
+
+Press Download now
+
+Rename the file to base.png
+
+convert base.png -crop 128x128+0+0 reload_scaled.png
+
+and use the make_spinner.py . Note that the results aren't very good.