Fix confusion in theme picker functions
To reproduce the bug currently: click on the theme picker button twice (to show it then hide it). Then click anywhere else: the dropdown menu appears again.
The problem was coming from a confusion of what the `hideThemeButtonState` and `showThemeButtonState` were supposed to do. I switched their codes and updated the `switchThemeButtonState` function. It now works as expected.
r? @kinnison