MeshMS RESTful API stricter on incoming form data

/restful/meshms/SID/SID/sendmessage now enforces Content-Disposition:
form-data (was ignoring), and enforces Content-Type: text/plain;
charset=utf-8 (was ignoring)

New negative test cases to ensure that these are treated strictly
MeshMS Java API: send message
New HTTP RESTful requests: MeshMS read message(s)
MeshMS Java API: mark messages as read
Merge latest MeshMS Java API additions into 'development'