Restructure sensor message format

[zsoltmazlo]

In this wiki page, the messages are sent individually for each train and wagon, which is a difficult task to collect in a receiver component. Thus, I'm suggesting the following format:

Message format:

JSON field	Type	Description	Example
time	int	timestamp of the message in milliseconds	1508578744987
locomotive	string	name of the locomotive	Taurus
length	float	the length of the locomotive	21.47
speed	cm/s or mm/s	the speed of the locomotive, only cm/s or mm/s could be used	10.67
unit	cm or mm	the length unit used in both the calculation the length and the speed field	mm
wagons	array of wagon objects	wagon message for each wagon, could be empty	[]

Wagon object:

JSON field	Type	Description	Example
name	string	name of the wagon	Red
length	float	the length of the wagon	21.47
unit	cm or mm	the length unit used in calculating the length field (it is recommended to be the very same unit which used in the parent object)	mm

An example message when a Taurus locomotive with two Red wagon passed by the sensor (disclaimer: the example data might not be real):

{
   "time": 1508578744987,
   "locomotive": "Taurus",
   "length": 21.47,
   "speed": 10.67,
   "unit": "cm",
   "wagons": [
      {"name": "Red", "length": 12.01, "unit": "cm"},
      {"name": "Red", "length": 12.07, "unit": "cm"}
   ]
};

This message format is open for discuss, please, comment on this issue if you have any ideas.

[zsoltmazlo]

As @hegyibalint pointed out, to discuss this issue it's enough to request review with tagging users a comment, thus all unnecessary assignment was removed and hereby I'm requesting review from the following users: @hegyibalint @imbur @baloghlaszlo @benedekh.

[szantob]

New json message added on "\modes3\locomotives" mqtt channel.
{ "sender": "sensor02", "time": 100, "locomotive": "Vagon", "length": 15.1454, "speed": 29.88464, "unit": "cm" }