[FIX] hr_timesheet_sheet: display timesheet by day summary in employee tz

If an employee in UTC + 1 (Europe/Brussels) entered an attendance from January 2 00:00 to Januay 2 23:59, the summary by day table displayed two different lines, for two different days:
 - 1 hour on January 1 from 23:00 to 23:59
 - 22:59 hours on January 2 from 00:00 to 22:59

 Which is obviously wrong, the employee, in its own time zone, worked on January 2 only.