[Sprint #2] init groups app and update user model

## Development Date
- 140731 - 140806 ( 7 days )

## Changes from previous versions
- we have changed our Model `Organizations` name to `Groups` -> generated new app called `groups`
- we thought `is_org_admin` field should be managed by `Groups App` -> deleted from previous `Users App`

## Features
1. Complete `Users App`
  - validate `phonenumber` field
  - user CRUD
  - login / logout / session feature
  - user permission
2. `Groups App`
  - basic `group` modeling
  - MtoN relational mapping ( `User Model` ~ `Groups Model` )