rework issue #553: modfied the name and the meaning of the three additiona...
rework issue #553: modfied the name and the meaning of the three additiona keys in the main header of the FitsFile version 1.21. They now refers to user (#578)
offset not subscna offsets.
issue #530 - New Fitszilla versione 1.21 online. The subscan offsets related keywords added to the primary header.
issue #533 - New Fitszilla versione 1.21 online. The user offsets related keywords added to the primary header.
issue #556 - Added API to send emails to local system administrators. This feature is now exploted when a servo system oscillation is detected at Noto and Medicina
## Fixed
issue #518 - In case of communication error we set a dummy value (100000) for the temperature properties, and the related timestamp keeps the value of the last communication timestamp.