hr_timesheet_invoice - extension

[Ferdinand]

the attached module allows to specify invoice date and a prefix for the invoice text instead of the hard coded "today()"

usually analytic accounts will be billed AFTER the end of a month, quater or year.
In Austrian it is usual and REQUIRED for VAT purpose to issue the invoice using the last date of the period AND to specify the period of service

the option in invoices to define a "periode" (month) which is different from the invoice date will not be understood and hence lead to different VAT periods used by suplier and customer which is against law as it opens doors to fraud.

IMHO this module should be integrated into the base code, because the wizard is not designed to allow inheritance without copying the complete code and hence difficult to maintain.