Feature/share shown in all projects

https://www.openproject.org/work_packages/8227

Adding the shown_in_all_projects property to query was necessary because previously a query was visible in all projects if its project was set to nil. This worked ok when we have a separate save view for the query but it doesn't work anymore because the retrieve_query method assigns the currently scoped project to the query. The result is that it wasn't possible anymore to know if a query in fact had a nil project anymore.

An alternative would have been to change retrieve_query so that it didn't scope the query and then take care of the scoping in the front end but this would have broken a shitload of other stuff that uses retrieve_query and i didn't fancy fixing all the test etc.

Ultimately it's not that important because Marek is going to re-write all the query logic at some point soon.