show_entry in user_interface.py uses wrong keyword argument for showSubmitToHexr

[Brendan Donegan]

This bug is unlikely to be hit, since it only happens when running Checkbox in headless mode *outside* of the lab/satellite environment, but we should fix it anyway.

show_entry is declared as:

def show_entry(self, text, value, label=None, submitToHexr=False, previous=None, next=None):
        return (value, submitToHexr)

but the code in checkbox-certification that calls it uses 'showSubmitToHexr'. This is the correct name, so user_interface should use it.

We also need to fix the other UI classes a little bit, as there's some oversight in the CLI and possibly Urwid versions too.