[Feature request] Make PIL/Pillow optional

[depau]

I'm trying to run OctoPrint on PyPy on ARM and it's being a pain because this module, which I don't want to give up, depends on Pillow and it won't run on PyPy on ARM (I opened an issue python-pillow/Pillow#2850).

I gave a look at the code and it seems to me that Pillow can be made optional. It's only used to flip the pictures from the webcam and to scale down profile pictures.

I think these features can be disabled if Pillow is not installed (original propic is used, no h/vflip feature)

What do you think?

[derpicknicker1]

Thats an option to think about. But when i remove pillow from the plugin requirements, it will not automatically insatll pillow for users which can use it.

[depau]

Users can simply install it manually. But I see some users might not know how to do it. Maybe we can just make an extra "fake" plugin that depends on OctoPrint-Telegram and Pillow so it gets pulled in.

[depau]

Other alternate solutions for this issue that came to my mind in the last few days:

• Pillow can be made optional in the code but setup.py can still depend on it. Users that don't want to use it will have to handle the unresolved dependency with pip on their own.
• The plugin may detect the pillow ImportError and not use it.

I will try to implement one of these and send you a PR as I would like to use it in my setup, feel free not to merge it if you don't like the workarounds (I would not blame you for that, this is definitely not an OctoPrint-Telegram issue).