XER: proj_node_flag is not being set

[Petr Janeček]

When writing XER files with mpxj, the proj_node_flag in WBS section is currently always false. The flag should be true when the WBS is a root node of a project. Oracle Primavera Cloud currently requires this.

In single-project files, this means when parent_wbs_id is null, proj_node_flag should be true.
In multi-project files, this is of course more interesting and the easiest naive rule, I think, is that if the parent WBS is from a different project, the proj_node_flag should be true.

[Jon Iles]

I've updated MPXJ to handle the single project case, so the proj_node_flag should be set appropriately.

[Petr Janeček]

Thank you for your continuing support!