A new generic authority connector for JSON data exchange format

This is a pull request from Guylane Bassette:

https://github.com/apache/manifoldcf/pull/159

The current MCF generic authority connector is taking XML for input. As time goes, JSON is now another frequently used data exchange format. So I have created a new generic connector, able to take json as input, instead of XML. Would you be interested in integrating it into ManifoldCF? The corresponding documentation can be found here: https://datafari.atlassian.net/wiki/spaces/DATAFARI/pages/2835021825/New+generic+authority+connector

Additionally to this new connector, I have fixed a syntax error in csv connector pom.

So we could consider this contribution for ManifoldCF 2.28.