main/py-pillow split to py3-pillow and py2-pillow packages

After version 7.0.0, Pillow does not support python2, therefor it makes less sense to have 1 single APKBUILD file for both packages.

Suggestion:

split py-pillow into testing/py3-pillow with the newest version and testing/py2-pillow with the latest 6.x.x version.

I already have working APKBUILD files and if this proposal is accepted, I can open the needed MRs.

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