[webui] remove person model - users rule them all
Merge pull request #437 from coolo/remove_person

[webui] remove person model - users rule them all
[api] mount the webui engine as /

- the default mimetype is application/xml if no Accept was given
- everything not default and not XML will go to the webui engine
- the rest stays in API

(remove HTML namespace as unused and all_routes_test because it's
just hiding missing coverage)