The light version of github data download/analysis tool

This release is for GithubUser part, so far it achieves the following things:

1. Task
   Divides big task into small ones.
   The tasks are stored in database.
2. Account
   The free account is very important for people who using openAPI.
   We store all the free accounts in database
3. Database
   Using mongodb currently.

There are still bugs. But it works very good to be honest :)