Colons in filenames getting errored in get-transfer

[jackleland]

If a filename has a colon in it then it will fail to be transferred when get-requested as the split(':') command invoked when reading the object_name from the PathDetails will result in more than 2 parts. We can either

1. Exclude filenames with colons in them
2. Use a different separator for the object_name e.g. ':::'
3. Accept that it can be split into more than two parts and put some verification in on the bucket name extracted

(1) seems unnecessarily restrictive, (2) may require a migration for existing records, (3) is probably the best choice?