add phonenumber to users.User
add validation for phonenumber
update user model : delete is_org_admin field
change user model name : users to objects as default
refactor users test
add teams app
add README : teams app features
add teams app to settings.py
Merge pull request #7 from dobestan/develop

[Sprint #2] init teams app and update user model
add invalid code into validation error
change test_phonenumber.py
add password field into REQUIRED_FIELDS
add, change invalid phone number variable
add regex validation method for phone number
add regex digit validation for phone number
add get_user method for user models
add test code for Retrieve user(get_user)
add test code for delete_user
complete get_user method
update test code for delete_user