Desktop Feature: Add back button for settings window

[PopCat19]

I was confused that I thought I had to restart the app every time I wanted change the settings before finding out esc was the key to return. It would be convenient to utilize mouse5 button to esc key and a back buttons.

I also drafted a button placement concept below:

I don't have much experience with Material Design but I hope this suggests an alternative way to return to the main page for people who only uses mouse to navigate.

[toasterofbread]

Mouse back is already implemented, it just doesn't seem to work on Windows for some reason. This should be fixed when #241 is merged.

In-UI back buttons for subpages are also planned.

[toasterofbread]

Navigating back with the mouse (or a custom key) should work now

[toasterofbread]

This was implemented by 05e593b