Extend 'pack' feature by adding option to keep repo's hierarchy, and warn about external deps.

`bam_cli.py pack` command now takes two more (optional) parameters, one
to specify the base directory of the repository, and one to enable
warnings when 'external' dependencies (to given base dir) are found.

Note that by default, base directory is the directory of the packed
.blend file (such that default behavior does not change at all).

See CLI help for more.

bam/cli.py

@@ -1329,8 +1329,10 @@ class bam_commands:
             paths,
             output,
             mode,
+            repository_base_path=None,
             all_deps=False,
             use_quiet=False,
+            warn_remap_externals=False,
             compress_level=-1,
             filename_filter=None,
             ):
@@ -1380,8 +1382,10 @@ class bam_commands:
                 output.encode('utf-8'),
                 mode=mode,
                 all_deps=all_deps,
+                repository_base_path=repository_base_path.encode('utf-8'),
                 compress_level=compress_level,
                 report=report,
+                warn_remap_externals=warn_remap_externals,
                 use_variations=True,
                 filename_filter=filename_filter,
                 ):
@@ -1763,6 +1767,15 @@ def create_argparse_pack(subparsers):
 
        # pack a blend with maximum compression for online downloads
        bam pack /path/to/scene.blend --output my_scene.zip --compress=best
+
+    You may also pack a .blend while keeping your whole repository hierarchy by passing
+    the path to the top directory of the repository, and ask to be warned about dependencies paths
+    outside of that base path:
+
+    .. code-block:: sh
+
+       bam pack --repo="/path/to/repo" --warn-external /path/to/repo/path/to/scene.blend
+
     """,
             formatter_class=argparse.RawDescriptionHelpFormatter,
             )
@@ -1780,6 +1793,15 @@ def create_argparse_pack(subparsers):
             choices=('ZIP', 'FILE'),
             help="Output file or a directory when multiple inputs are passed",
             )
+    subparse.add_argument(
+            "--repo", dest="repository_base_path", metavar='DIR', required=False,
+            help="Base directory from which you want to keep existing hierarchy (usually to repository directory),"
+                 "will default to packed blend file's directory if not specified",
+            )
+    subparse.add_argument(
+            "--warn-external", dest="warn_remap_externals", action='store_true',
+            help="Warn for every dependency outside of given repository base path",
+            )
 
     init_argparse_common(subparse, use_all_deps=True, use_quiet=True, use_compress_level=True, use_exclude=True)
 
@@ -1791,8 +1813,10 @@ def create_argparse_pack(subparsers):
                     ((os.path.splitext(args.paths[0])[0] + ".zip")
                      if args.mode == 'ZIP' else None),
                     args.mode,
+                    repository_base_path=args.repository_base_path or None,
                     all_deps=args.all_deps,
                     use_quiet=args.use_quiet,
+                    warn_remap_externals=args.warn_remap_externals,
                     compress_level=args.compress_level,
                     filename_filter=args.exclude,
                     ),