Individuals: Selecting/unselecting single individuals does not work

[hannamlmv]

When a single individual is unselected on the individuals page, that modification will not be saved if you go to another page and then back to the individuals page.

It could be useful to be able to select not just entire sample sets but also specific individuals as mentioned in this comment by Per: "It might be good if the user could also select individuals on an individual basis, i.e., click the cross mark column in the individuals table (this has no effect right now, right?). A hacky workaround is to generate a dummy sample set, move selected individuals there (is that possible btw?), and exclude that sample set from rendering. These issues could be solved in separate pull requests."

I could not find an issue about this, if there is a duplicate we can remove this one.