Extend Kernel to support <file_order_source> attribute "alert_when_directory_missing"

• Using <file_order_source> if the monitored directory does not exist you get error ERRNO-2 No such file or directory by default.
• When in factory.ini "mail_on_error" is set to "yes" then also an error mail is sent.
• The JobScheduler tests periodically if the missing directory exists.
• If the missing directory is found you get an recovery-mail to inform you that the missing directory now does exist.
• Now the directory can be used for file orders as usual.

The alerts can be deaktivated:

• If you set the <file_order_source> attribute alert_when_directory_missing="no"
• No error message and no mails are sent regarding the missing or new created monitored directory.

Possible values for alert_when_directory_missing are "yes" or "no" (default=yes).