Create ApplicationForm controller

[avishkar58]

Depends on #18

Create a back-end controller that can be used to GET an application form.
GET should be able to retrieve an application form for a given eventId

POST is optional for now because we could insert the data for the Indaba2019 form directly into the database in the interim.

Example of JSON response:

{
"eventId": 1,
"is_open": true,
"deadline": "2019-04-30",
sections: [
{
"sectionId": 1,
"name": "Section 1",
"description": "Section 1 description",
"order": 1
"questions": [
{"description": "Question 1", "type": "short-text", "required": true, "order": 1},
{"description": "Question 2", "type": "single-choice", "required": false, "order": 2},
]
},
{
"sectionId": 2,
"name": "Section 2",
"description": "This is section 2",
"order": 1
"questions": [
{"description": "What is 2+2?", "type": "short-text", "required": true, "order": 1},
{"description": "Upload your CV", "type": "file", "required": false, "order": 2},
]
},
]

}

Definition of Done
This task is done when:

• There is an implementation of an applicationForm API in api/app/applicationForm/api.py that accepts a GET request
• The API correctly retrieves the applicationForm (and associated section and question) models from the database
• The API serializes the applicationForm and associated models and responds with JSON conforming to the above example
• There are unit tests for the API