Non-obvious changes include:

 * Adopt the "GNOME screen keyboard" and "screen keyboard" terminology, (as
   opposed to "virtual keyboard"): that's how this feature is called in the
   Accessibility menu and everywhere else in GNOME. The only exception is the
   doc/encryption_and_privacy/virtual_keyboard page, that I didn't bother
   rename: I bet sajolida would rename it again to give it an even better name
   anyway ;)

 * Drop corresponding doc in the intro to GNOME: we only have to present the
   elements visible on screen when starting Tails, and there is no such element
   anymore for the screen keyboard.

 * Drop the picture as I don't think it's needed: once enabled, the screen
   keyboard is so visible one cannot really miss it.