Add account switcher to system tray context menu

[0xqiba]

This change adds an Accounts submenu to the system tray menu for switching between accounts without having to bring up the main Frame window. It also now shows the keyboard shortcut, if enabled, next to the Summon/Dismiss menu item.

As part of this change, I removed some multiple display handling code (switchScreen in systemTray.ts). In my testing, it didn't seem to have any effect, but please let me know if I'm mistaken.

Happy to iterate on any feedback you may have. Thanks!

[floating]

Thanks @0xqiba will give this a look!