Feature/issue 15 user opinions exposed via json

Fix #15 

Done
-------------------------
- Created opinions directory and added it to settings.
- Added Opinion model.
- Did Schemamigrations on it
- Added API path to urls.py
- Created unittests for API
- Coded the API and made sure it works.

Assumptions
---------------------------
- The API spits out data in the form of `"opinion_1": "This is opinion 1"` as opposed to  `"1": "This is opinion 1"`
- There is always going to be an opinion hence a situation where there is no opinion has not been considered i.e. {"There is no opinion this week"}.