#154 Introduce Workorder.PrintCount

[Steffen Macke]

Current SVN head version.

Instead of querying for an empty history table,
a new integer field Workorder.PrintCount should
be introduced and increased every time print_workorder.php
is invoked.

This will improve the application logic when deciding
if workorderpage.php should forward to
print_workorder.php (Workorder.PrintCount = 0).