Schema refactor

### Tables
- repository
- user
- repository_user
### repository

> Information about the github repository. The data will be updated every N hours
- Id
- gh-id
- stars
- name
- description
- language
### user

> Information about the github user.
- id
- gh-id
- name
### repository_user

> Tracks which users are subscribed to which repos
- id
- repository_id
- user_id
- last_stars
