Sent a message

[iuresti]

Create endpoint POST /api/message with body:

{
     "title" : "subject of the message",
     "highPriority": "true/false",
     "body": "A message encoded in base64",
     "receivers":["userId1", "userId2", "userId3"],
     "resources": [
         {
               "mimeType": "standard mime type",
               "payload": "byes of the attachment encoded in base64"
         }
     ]
}

• Use current date as send date
• Use current user as sender
• Receivers must not be empty
• Resources can be empty or even not to be present