Pressing Ctrl-S should save the project #4262
Description
Expected Behavior
Ctrl+S is a really common keyboard shortcut in almost any program, so pressing it should cause Scratch to save the project (just like pressing the "Save Now" button).
Actual Behavior
Ctrl+S doesn't do anything in Scratch 3.0 (it just opens the browser save-page-as dialog which, yes, can be overridden).
Steps to Reproduce
Press Ctrl+S while in the 3.0 editor.
Operating System and Browser
Firefox 65.0b7, Linux (Debian).