Resolve "Refactor the relationship between FileBrowser, various entry/upload views and their contexts"

Final part of the refactor #828 (closed). The main idea is that instead of passing around changing context parameters in the browser, we use the data store, which acts like a kind of central cache/context, and we make sure that components keep track of urls indicating "where they are", and use these when they need to resolve any references etc. The resolving logic is also made more explicit, by instead of methods like resolveRef and resolveRefAsync using methods with a bit more narrow functionality and clearer and well-documented interface. Usually resolving a reference is now a two-stage process, first using resolveNomadUrl to calculate a url and then using the store to fetch the data, which forces the code to be very specific/explicit. Also fixes some sporadically failing gui and python tests.