Delivery rework

Clean up destination code and add some functionality

• Split the destinations into separate files
• New DestinationTempFile for writing tempfiles into the destination which eventually get added
• All of the close() methods are now streaming
• Implemented ChecksumDecorator, so we get a SHA1SUMS file
• Implemented FetchFile decorator, so we get a rudimentary fetch-all.sh script
• Configured Docker and delivery for local development to have a separate volume mount for serving files

apps/cli/executables/delivery/delivery/destinations/checksum.py

@@ -32,6 +32,11 @@ class ChecksumDecorator(DestinationDecorator):
 
     @staticmethod
     def hash_file(file: pathlib.Path):
+        """
+        Hash the supplied file
+        :param file: file to hash
+        :return: string in SHA1SUMS format (hexdigest)
+        """
         # You would expect performance to be worse than calling a C program here, but in my own testing I found
         # that the ensuing block is somewhat *faster* than calling "shasum" directly. I was able to hash a 1 GB
         # random file in 1.2 seconds with the following code, versus 1.8 seconds with shasum. This is across about 10