Add Crowd as a new identities and affiliations data source for GrimoireLab (still managed by SortingHat)

This is a feature request. The goal of this is to integrate [Crowd](https://www.atlassian.com/software/crowd) information in GrimoireLab and use this tool as the trusted data source for identities, and affiliations.

Crowd is used by several and different open source communities, and internally at some corporations. SortingHat already supports some specific formats, but not this tool.

In this case, this sounds to me that SortingHat should be pulling information from Crowd (or the other way around) from time to time to keep updating the identities.

Corner cases I see in this development:
* There are several ways to interact with SortingHat: identities file, Hatstall, importing JSON docs, and pulling information from Crowd (if this development is done). There should be somewhere a clear hierarchy of actions so one tool (e.g., update through Hatstall) do not overlap others (update in Crowd).
* SortingHat may not be the tool directly pulling info from Crowd, but some tool in the middle as SortingHat does not do this.