Formatted image file data structure that breaks down by subdir (#1102)

- New utility method for the web app, which sorts image files into dicts where the subdir is the key
- In the web ui, display each subdir in a table nested in a details tag.
- Allow for picking destination subdir when uploading files
- Style the expandable details blocks in the images table
- Add a check for ~ paths to the is_safe_path() utility method

python/web/tests/api/test_files.py

@@ -254,6 +254,7 @@ def test_upload_file(http_client, delete_file):
 
             form_data = {
                 "destination": "disk_images",
+                "subdir": "",
                 "dzuuid": str(uuid.uuid4()),
                 "dzchunkindex": chunk_number,
                 "dzchunksize": chunk_size,