fix referee invitations and reminders to use email

scipost_django/templates/email/referees/invite_contributor_to_referee.json

 {
     "subject": "SciPost: refereeing request",
     "recipient_list": [
-        "referee.user.email"
+        "email_address"
     ],
     "bcc": [
         "submission.editor_in_charge.user.email",

scipost_django/templates/email/referees/invite_contributor_to_referee_reminder1.json

 {
     "subject": "SciPost: refereeing request reminder",
     "recipient_list": [
-	"referee.profile.email"
+	    "email_address"
     ],
     "bcc": [
 	"submission.editor_in_charge.user.email",

scipost_django/templates/email/referees/invite_contributor_to_referee_reminder2.json

 {
     "subject": "SciPost: refereeing request reminder",
     "recipient_list": [
-	"referee.profile.email"
+	    "email_address"
     ],
     "bcc": [
 	"submission.editor_in_charge.user.email",

scipost_django/templates/email/referees/invite_unregistered_to_referee_reminder2.json

 {
     "subject": "SciPost: refereeing and registration invitation reminder",
     "recipient_list": [
-	"jscaux@"
+        "email_address"
     ],
     "bcc": [
         "edadmin@"