addressing comments

* add scratchLogo as default for logo prop
* prefer `{featureAllowed && (<Component />)} over ternary operator with a null ‘else’
* renamed `handleSaveToComputer` as `getSaveToComputerHandler` to more clearly represent what it’s doing (returning a function to be the handler)
* renamed the parameter that is the function to handle clicking on the load project menu item (also updated the comments in `SBFileUploader`)