Include "has_verified_email" flag in IdentityJsonTemplate.

Include `has_verified_email` flag in `IdentityJsonTemplate` so that when you make a `GET` request to `/user/<username>/about.json`, the JSON response includes the flag that tells whether or not the user has successfully verified their email address.

    {
        "kind": "t2",
        "data": {
            "has_mail": false,
            "name": "reddit",
            "is_friend": false,
            "created": 1364192756.0,
            "modhash": "reddit",
            "created_utc": 1364189156.0,
            "link_karma": 1,
            "comment_karma": 0,
            "over_18": false,
            "is_gold": false,
            "is_mod": true,
            "has_verified_email": true,     <------------ this
            "id": "1",
            "has_mod_mail": false
        }
    }

The motivation for this change is to encourage users to provide and verify their email address in the event they get a `QUOTA_FILLED` error from a link submission. API clients may inspect a user's `has_verified_email` flag to determine whether or not to recommend the user to update their email address.