Use Pillow to handle images

[anuschka]

As in this tutorial:

http://pillow.readthedocs.org/en/latest/handbook/tutorial.html

[ialja]

Btw, Pillow is already in use.

[anuschka]

You are totally right @ialja 👍 but we could perhaps think about 💭 (next release) using some of its image manipulation features in TrackCat.