Add informations about the GPS data

[ebocher]

On the map viewer and in the app, some informations must be added to explain the main constraints on the GPS data. eg. If the GPS accuracy location is greater than 15 meters the data will not collected on the server. eg. What about the maximum speed ? ...

[nicolas-f]

There is currently no filter on maximum speed. Such filter may require the computation of median speed for each track.

[pierromond]

#280