Replaced BAM with BAT

Blender Asset Tracer, or BAT, is a newly written replacement for BAM,
with a nicer API.

blender_cloud/flamenco/bat_interface.py

@@ -0,0 +1,35 @@
+"""BAT🦇 packing interface for Flamenco."""
+
+import asyncio
+import logging
+import typing
+from pathlib import Path
+
+from blender_asset_tracer import pack
+from blender_asset_tracer.pack.transfer import FileTransferError
+
+log = logging.getLogger(__name__)
+
+
+async def bat_copy(base_blendfile: Path,
+                   project: Path,
+                   target: Path,
+                   exclusion_filter: str) -> typing.Tuple[Path, typing.Set[Path]]:
+    """Use BAT🦇 to copy the given file and dependencies to the target location.
+
+    :raises: FileTransferError if a file couldn't be transferred.
+    :returns: the path of the packed blend file, and a set of missing sources.
+    """
+
+    loop = asyncio.get_event_loop()
+
+    with pack.Packer(base_blendfile, project, target) as packer:
+        if exclusion_filter:
+            packer.exclude(*exclusion_filter.split())
+        log.debug('awaiting strategise')
+        await loop.run_in_executor(None, packer.strategise)
+        log.debug('awaiting execute')
+        await loop.run_in_executor(None, packer.execute)
+        log.debug('done')
+
+    return packer.output_path, packer.missing_files