Add the possibility to store the cut values for the different formats

[OlivierMarchal]

The different cut values are not stored in memory so everytime a user changes the format from 'png' to 'fits' and then back to 'png', the default values are restored.

To reproduce the problem :

1. go to https://aladin.cds.unistra.fr/AladinLite/doc/API/examples/AL-in-responsive-div/
2. Choose for example Panstarrs dr1 g and select format = 'png'

3. set mincut to -1
4. set format to 'fits' then back to 'png' : the mincut is now 0, the default value, and not what the user set before.