Embed oracle in node as subcommand

Make the distance oracle a duniter's subcommand, to make distribution and installation easier.

Duniter client would, given a --distance-oracle option, automatically run the oracle as a separate process.

added C-binary D-medium ET-days P5-sometimesoon RN-binary S-ToDo labels

assigned to @tuxmain

mentioned in merge request !225 (merged)

closed with merge request !225 (merged)

removed S-ToDo label

mentioned in merge request !267 (merged)