Support to annotate photos on other than macOS OSes

[ligurio]

dogsheep-photos allows to annotate photos using Apple Photo's db. It would be nice to have such ability on other OSes too. For example using trained local model or using Google Vision API (see #14).

[ligurio]

There are trained ML models used in Photoprism:

• https://dl.photoprism.org/tensorflow/nasnet.zip
• https://dl.photoprism.org/tensorflow/nsfw.zip