Feature Request: Full History/Custom save location

This differs from https://github.com/divamgupta/diffusionbee-stable-diffusion-ui/issues/24 because there already is a history, however it only saves within the current application session.

I request the history is kept across openings or provide a custom save location for every generation.

A brainstormed folder structure:

Directory: DiffusionBeeGenerations/
- Generation-{ timestamp/UUID }
- prompt.txt
- image1.png
- image2.png
- image3.png
- ...
- Generation-{ timestamp/UUID }
- prompt.txt
- image1.png
- ...

Where **prompt.txt** contains the single-line prompt for that generation.

This would also be a change in behavior of how images are saved since they are already saved on generation, however this is open to complete customization as it sees fit.