[NODEJS-1598] PoC of acs-node-sdk Rework

## Ticket Information
***JIRA Ticket***
https://jira.appcelerator.org/browse/NODEJS-1598

***Description***
This PR is about to raise a PoC of ACS Node SDK rework. It re-designs framework of acs-node-sdk, and supports multiple instances. It also provides a way to list all available ACS objects and methods including doc url for a good reference. Test framework with travis-ci is added too for a good and automatic test.

Since this is only a PoC, I only implemented ACS object "Users". If this way is towards to a good direction and passes code review, we will add all other ACS objects later.

## Get started
Please refer to readme file https://github.com/realpaul/acs-node-sdk/blob/NODEJS-1598_ReworkPoC/README.md for a general usage.
Thanks Simon for your suggestion and I have updated code. It is much clearer right now:
```
  Users Test
	Generated acs user: acsuser_81268cfdfe
    .queryAndCountUsers
      ✓ Should return all users (2109ms)
	Current users count: 8
      ✓ Should return the correct user number as queried before (1397ms)
    .createUser
      ✓ Should create user successfully (2138ms)
	Current users count: 9
      ✓ User count should be increased (1274ms)
    .loginUser
      ✓ Newly created user should be able to login successfully (1941ms)
      ✓ Should show logged in user correctly with stored cookie string (1302ms)
    .deleteUser
      ✓ Should delete current user successfully (1758ms)
	Current users count: 8
      ✓ User count should be decreased (3670ms)


  8 passing (16s)
```