reactivate at same zoom position

[mfrasca]

remember, Android has a very smart way to address multitasking: per default tasks in the background get swapped away and get started back again when requested to the foreground.
in practice, programs are forcibly stopped and restarted.
to get back to where we were, we need use that bundle object that we can fill when we are stopped and that we are handled back when we are restarted.
so we should include in the bundle:

• zoom level
• centre of the map
• active garden (if any)
• active panel (if any)
• what am I forgetting?