Create backend API

[shari09]

GET requests:

• get board page (load a selective amount of posts per request -> pagination)
• get post popup
• "add new post" page

POST requests:

• add a new post to a board (must contain either at least one photo or a message, name is optional)
• verify that the uploaded file is an image

Create the views.py file under the app/ and look into Django generic views to reduce redundancy.

[shari09]

TODO:

• [x] board details
• [ ] image
• [x] main board
• [x] get posts
• [ ] create posts