enhancement: close project #3312
Description
It would be nice with a button to (save and) close the current project (all windows and datafiles). To clean the slate for new tests and fits etc. Just like it has been introduced in the new ATSAS 4.0.1 (e.g. in primus or chromix). Thus everything can be cleared without having to close and reopen SasView, which can be a bit slow.