Removed code duplication by introducing a timesheets() php function that will be called from every timesheet overview type (status: all=-1, open=0, submitted=2, approved=3).

- Changing status and period of timesheet doesn't create 2 timesheet now. It only creates one timesheet or updates the current timesheet.

Feature added:
- Added a new row timesheet_worked to database for keeping a total of hours worked that timesheet_period.
- Added row timesheet_worked to inteface.

Make delete, changing status and period work. Make status and period fields in addedit.php readonly when the timesheet has been submitted and approved.

TODO:
- delete from vw_idx_*.php files doesn't work.
- changing status and period on new file creates a duplicate record.

TODO:
- deleting
- updating
- admin mode
- adding project hours and total to timesheet