created basic CRUD operations for rest of all models

[sanghunjo921]

issue: #12

created CRUD operations for user, preferredProperties, agent, application and contract model

1. made serializers
2. made views
3. made urls

Refactoring: split models into a group that uses the same starting point for urls

todo: figure out how to make a urls.py when adding more than 1 id in a URL

[sanghunjo921]

user

[sanghunjo921]

agent

[sanghunjo921]

application

[sanghunjo921]

contract

[sanghunjo921]

preferredProperties