Remove pyyaml dependency
Created by: g-scott-murray
Replace pyyaml module usage in app bbclass code with re based parsing of the app name from pubspec.yaml. This avoids needing either pyyaml on the build host or mixing the host and -native Pythons as was being done. Also, a couple of the app name errors have been bumped to bb.fatal from bb.error to end building immediately, as do_compile is going to fail in those situations, anyways.