First working version (VCS untested)

Cache unadulterated signal names (don't add dut.name).
This will not work if we try to access signals for nested modules, but I don't think the current code supports that anyway. Add whatever prefix is required for the specific backend when we interrogate it for the actual signal.
Fix getDataNames() so it doesn't automatically add the top level name for an aggregate since these don't exist in some simulation environments (i.e., we need to synthesize them from their actual components).
Set the targetDirName something other than "."
Add scoping to resource names.
Support firrtl and verilator backends for BasicTest.scala.