Use original_filename to get the name of the file attached to the message. Had to add the message_type method to the WhatsApp/incoming_message_service due to the Assignment Branch Condition linter error for the attach_files method. Fixes #4183
MMS sent from an ATT or Verizon phone number seems to be appending a SMIL file in .xml format for MMS.
Ability to send and receive MMS to bandwidth channel fixes: #3961
fixes: #3888
