creating / saving FOV

[roccorollo]

1. a first issue is that sometimes one gets a pop-up window with error :
   local variable 'table' referenced before assignment
   I have obtained this error after asking for a second or third FOV, and waiting for the statistics window.
   The previous statistic window was closed with the "confirm" botton.
   (both Andrea and Giulia can replicate this)
   After that, one needs to re-start Aladin and GW-sky.

2. Second issue is that there is no backup: if someone confirms a new FOV, only pointings are kept, but all statistics is lost. It would be cool to have also queries of previous pointings saved, and be able to open with other tools, e.g topcat.
   It would be even wonderful to have the possibility to save also the statistic images (idea: a botton close to activate statistics).

3. If someone closes start FOV window, ans atsrts a new one, old FOVs poitings are lost. There should be a warning.