Change Favourite Behaviour to Use PUT/DELETE

[jenslauterbach]

Minor change as proposed by Jan to not have separate endpoints to favourite/unfavourite sessions, but to use PUT/DELETE on the same endpoint.

Now the output of /api/sessions/ and /api/sessions/<session-name>/ looks like this:

[
    {
        "id": "acheing-a-internally-attached-limit",
        "url": "http://localhost:8000/api/sessions/acheing-a-internally-attached-limit/",
        "title": "Acheing A Internally Attached Limit",
        "description": "Dolor quisquam modi magnam sit sed. Modi velit neque dolor. Voluptatem consectetur dolorem ipsum amet quaerat adipisci. Ut quiquia numquam adipisci. Modi tempora quisquam quiquia.",
        "speakers": [
            {
                "url": "http://localhost:8000/api/speakers/jana-vogel/",
                "name": "Jana Vogel",
                "image": ""
            }
        ],
        "event": "devdata.18",
        "actions": {
            "favourite": "http://localhost:8000/api/sessions/acheing-a-internally-attached-limit/favourite"
        }
    }
]

Run PUT http://localhost:8000/api/sessions/acheing-a-internally-attached-limit/favourite to favourite a session and DELETE http://localhost:8000/api/sessions/acheing-a-internally-attached-limit/favourite to unfavourite it.

[coveralls]

Pull Request Test Coverage Report for Build 1505481088

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 99.098%

---

Files with Coverage Reduction	New Missed Lines	%
talk/api_views.py	3	63.46%
<!--	Total:	3		-->

Totals
Change from base Build 1502732878:	0.04%
Covered Lines:	3805
Relevant Lines:	3841

---

💛 - Coveralls