Merged requested to merge payno/pypushflow:add_addon into master
Define and manage add-on to pypushflow.
/close #2 (closed)
This PR come with two add-on project:
- a project to explain add-on with an hello-world (https://gitlab.esrf.fr/workflow/ppfhelloworld)
- a functional add-on 'mongodb' to publish workflow execution on a mongodb database. (https://gitlab.esrf.fr/workflow/ppfmongodb)