Separated test cases into two classes
Removed 'company' param in config.ini

This parameter has a slightly confusing behaviour - it will show empty values
if a requested user exists, but doesn't belong to the company.
Mock local functions if possible, not libraries

This will make the transition to an async http request library easier.
Added requests-futures dependency
The user check now uses asynchronous requests
Rewrote 'check_users_exist', now returns list
Fix 404 error due to stackalytics API change

Stackalytics requests fail now when one of the user_ids in the people
parameters is unknown (it was previously ignoring them).
Increase max number of threads for user check