Manifest validation tool issues: file extension presence detection

[elopatin-uc3]

While working with UCI on their manifest-of-manifest submissions, we've noticed two issues in the validation tool:

1. The need for file extension in the nfo:filename is not caught. For example, if the URL for a file specifies myfile.tif, the corresponding entry in nfo:filename should be myfile.tif ("myfile" without an extension, should be flagged as an error)

Requires file extension to be present (OK)
When submitting a CSV with checkm files in the line entries, the type of manifest generated should be a mrt-batch-manifest. Currently, the validator creates a mrt-single-file-batch-manifest, which is not ideal.