Add key to `options_hash` for email: `plus_allowed`

[Hainish]

Technically, + is a valid character in the user string of an email address. However, some congressional form validators will reject such an email address at the point of submission. Concommitant with https://github.com/EFForg/congress-forms/issues/45, we should add a key to the options_hash for email fields with a key of plus_allowed, and a boolean value. This should be assumed to be true by implementations, unless specified as false.

[j-ro]

noting here that there are lots of weird validation rules we've hit on some fields. Like, some forms won't accept spaces or punctuation in name fields, so a name of "J. R." fails.

Not really sure what can be done about that. We don't have a lot that fail this way, but a small percentage. I guess maybe think about how to work in validation rules into the yaml schema, but maybe that's overboard.

[oregondean]

One solution is to advise the owner of the form that they have an unreasonably tight criteria on some of their fields ... and track their progress towards correcting their form.