Move shared queries to reusable functions

[AudunVN]

We have a lot of code that want the same data (e.g., a specific set of invoices or cruises), but a lot of these use completely separate model query instances. This makes code very hard to maintain, as there is no easy way to find out which queries you should update where if the definition of an object class changes (such as "unfinished invoices").

[AudunVN]

See also 2b8b54f, where I found out that we have five queries that should be identical for the "invoices that need admin attention" case with no obvious way to find and update them when things change.