Merged ManBuilder.staging_source_dir and MB.curation_source into manifest_source_dir

...s/pexable/ingest_envoy/ingest_envoy/ingestion_manifest.py

...xecutables/pexable/ingest_envoy/ingest_envoy/launchers.py

...tables/pexable/ingest_envoy/test/test_curator_manifest.py

...ables/pexable/ingest_envoy/test/test_evla_cal_manifest.py

...es/pexable/ingest_envoy/test/test_img_manifest_example.py

...e/ingest_envoy/test/test_manifest_builder_entry_points.py