Imperative code in belongings-related components

[gabrc52]

This is basically imperative code, leading to the sort of bugs that trying to write vanilla JS leads to:

I'd refactor this to use await blocks and take advantage of the fact Svelte lets you declare constants inside them (which was the reason I initially wrote the code like that, because I didn't know you could do that)

It's treating "loading" and "has error?" as two unrelated parts of state but they could be easily coupled with promises. Leading to this:

I think I'd already fixed a similar bug by changing some if statement but the advantage of writing declarative code is that you don't have to think about every branch.