Clone subset of files with filename list

[mzur]

As an alternative to the * wildcard, allow users to paste a comma-separated list of filenames in the clone volume form. This may be useful if users want to clone a random subset for QA/QC. Allow only one of the options, either the wildcard or the comma-separated list. Also validate that users can't submit more filenames than the DB parameter limit (or chunk a longer list in the backend).