Allow users to not override default mailer configs

Fix from_address logic in mailers, it broke when there were noe
mail_method record on the database

Fixes #2929
adding spec and fixing user_logged_in promo rule

Fixes #2884
Wait for API request to complete in stock management spec
Fix remove_fields link from stepping on cocoon

Because the cocoon gem defines a similar callback on 'document', this callback will effectively override it.  
Modified selector scope to ignore cocoon links as a primitive workaround.

Fixes #2853