Parse assistant information from message array.

[barelyknown]

Find the last assistant that that sent a message and assign set them as the assistant that performed the task.

This is a feature that wasn't originally available, but is now in the message object:

{
 messages: [
 {
 assistant_key: "ahBzfmZhbmN5aGFuZHMtaHJkcgwLEgZGSFVzZXIYAQw",
 assistant_name: "Ted R.",
 content: "test: this is the answer\n\n",
 content_type: "text/plain",
 date_created: "2015-08-14T16:42:28.643610",
 local_date_created: "2015-08-14T12:42:28.643610-03:00"
 }
 ]
}