Main.cpp, Nook.cpp: Initialise internal TTY port on Nook

This keeps TopHat in the Android foreground when
the superuser authorization popup appears
the first time TopHat is run after installation
on a device.
Startup.cpp: move Nook initialization to after screen initialization

This allows Androids "Allow superuser" popup to show after TopHat's
main screen is created, so when the popup disappears, TopHat
remains in the foreground.