Use native font stack for desktop app UI

In my opinion the Roboto font is kinda bad for displaying the app on the desktop. As more and more websites are increasingly using the native font stack (i.e. -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Ubuntu", "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"), I think we should change the display font on the desktop app into the native font stack.