Store some/all settings

Currently all settings are lost on page reload. This is especially annoying, if one uses custom colors and has to change them again.

I already implemented storing/caching of person data from the dataset, extending it to include settings is trivial.

There are however two questions:

1. What to store and what better not to store? example: If I mess up the filters, currently I can just reload.
2. Do I have to ask the user for permission. As far as I know, I am required (by eu cookie law) to ask the user before storing any data that is attached to an identity. Maybe custom (colorblind) colors count?

@nprobst what do you think? Maybe I should ask for permission just in case? Better safe than sorry? Personally I always sigh when a websites asks me to store stuff... 🤷