xmlui: count with timeshifts when registering gateway
xmlui: count with timeshifts when registering gateway

The gateway registrations contains also a time zone specification.
In XML-UI, we specify time zones by UTC offset. The 3600 should be
mapped to CET. However, during the summer period, the offset for
CET is 7200 and thus returned value is different.

Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server