Find a way to display on which endpoint requests are made

Since singleton refactoring, the:

print("Requested node: <{}:{}>".format(ep["domain"], ep["port"]))

node requested information is displayed twice if put in EndPoint class.

We should find a way to display it back again, or at least with the logging tool.

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With DuniterPy ConnectionHandler.__str__(), with some improvements (adding the path…)