Using Zanata RESTful API in tools/zanata/*.py

Using Zanata RESTful API instead of web crawling in zanata utilities.

1. zanata_users.py
1-1. test zanata api
1-2. make method(s) of using zanata api
1-3. test method(s) of 1-2
1-4. change web crawling method(s) to 1-2
1-4-1. get projects list
1-4-2. get versions of each projects
1-4-3. get contributers of each versions of projects
1-4-4. sort contributers
1-4-5. make translators list just like as web crawling methods
1-5. test 1-4
1-6. clarify my code
1-7. review

2. think 1. first.