redesign namespace extensions

[sgratzl]

In the current version, plugins can register namespace extensions that are essentially flask/wsgi applications. The question is whether instead of using annotations and objects that are fixed we use a plain annotation or declaration (swagger) approach.

see also connextion

In the current version, the plugins don't include flask directly anymore but 'phovea_server.ns' that rexports flask at the moment.

features needed similar to flask

• rest api functions
• access to parameters (request.args, request.values)
• form files access
• specify response type
• generator as response for streaming (either asynchronous definition or event-stream)
• websocket definition

[sgratzl]

django main request/response objects: https://docs.djangoproject.com/en/1.10/ref/request-response/

[sgratzl]

see also https://github.com/jfinkhaeuser/prance

[sgratzl]

see also https://github.com/zalando/connexion

[sgratzl]

first test under the feature_swagger branch. dataset, idtype, and last_deployment apis are changed. So, you can access: http://localhost:9000/api/dataset/ui/