Add an option to submetadata to allow filemappings to be transparent in and/or out of the submetadata

[autumnpat]

entering a submetadata block pushes a clean slate for metadata - which can be extremely annoying when the submetadata's (subproject, really) participates in and needs to refer to the filemappings in its parent project. and needs to pass filemapping back up to the parent project...

initially, the notion was that there needed to be a clean separation between subprojects/submetadata....which is still desireable when, say, four "unrelated" subprojects are built under a single project (which also ensures that the subproject could be built on its own), but in practice, having a way to pull in the parent mappings is wanted many times in my experience.

[autumnpat]

csmake-hpe#3