Kiosk mode

[JF Rameau <jframeau cyberdeck com>]

Hi,

many kiosks use touchscreen monitors, some without keyboard nor pointer. 
This is kind of accessibility problem i think.

Feedbacks from our users say:

- we need a button to close opened windows (in case users have this 
ability). Close button does not appear on root window (the first 
displayed) if enable_quit is false.

- for whom with visual impairments, we need some buttons to zoom 
(ctrl++, ctrl+-) accessible from toolbar.

jeff