User form changes

The user form should show more details for the user record.

1. Need to add few fields to form, few of them should be editable and few should be readonly.
2. Read-only fields: 
  - `sent_on`
  - `source`
  - `joined_on`
  - `subscribed_at`
  - `unsunscribed_at`
  - `opt_in_mail_sent_at` 
3. Fields that can be edited:  
  - `status`
  - `is_blocked`
  - `is_subscribed`