Evalutate what datasources will be deprecated in GrimoireLab 2.x

GrimoireLab 1.x supports more than 30 different datasources. Some of them like twitter or nntp don't work anymore. Others like telegram, phabricator, or groupsio haven't been updated and tested since long ago.

For GrimoireLab 2.x we're considering to have less core datasources so we won't have to maintain those not frequently used. We'll encourage and support the development of third-party backends that add support for other datasources.

The purspose of this task is to evaluate what datasources will be left out. These doesn't mean they are going to be removed from perceval but data won't be processed by the platform out of the box.