Alias emails

If a submitter changes his email account and still want to be able to access his old submissions. Setup and alias and return submissions on both emails when asking with one of them.

Start by tracing how submitter email addresses are used when submissions are queried. Determine where an alias could be stored and how lookups should treat both addresses; done means either email returns the submitter's old submissions without breaking existing queries.

Written by the indexing model from the issue text.