ModelForm endpoints

[atengler]

• add FormTemplateCollector client to get form source template (YAML, Jinja2, RST) and render it into JSON form schema with pre-generated secrets and HTML documentation
• add endpoints to expose the FormTemplateCollector

[katyafervent]

let's do not use requirements txt and keep everything in setup.py and use pipenv. You can generate requireents.txt with pipenv lock -r if you want

[atengler]

Pipenv doesn't really work for me and python setup.py install fails for me, because of the pygerrit installation fails with PBR error, so I wanted an alternative. But the PBR error can be worked around by setting PBR_VERSION=1.0.1-dev1 before running python setup.py install so I can remove the requirements.txt I guess. Just pointing out why I wanted to have one