When a CSV file fails to validate a user should be offered the option to re-validate using a different dialect

Fixes theodi/shared#146

When a CSV appears to fail to validate (that is, the `check_options` error is flagged), then the user has the opportunity to revalidate against a different dialect.

This works for URLs and files, as I'm now saving the contents of files to the DB using MongoDB's `GridFS` functionality. This will also work with large files.