Indicate origin of data in API results

[demeringo]

Problem

End user of the API would be interested in getting metadata, in addition to the impacts.

Solution

This is to be discussed in term of feasibility and if it could/should implemented on all routes or not.

• source of impact data
• date of last data refresh

Likely use it only through and extra verbose -optional- mode

Alternatives

Additional context or elements

[demeringo]

Closed as duplicate of #91