ME: added TempToken model
ME: added migration file for TempToken model
ME: added TempTokenAuthentication class
ME: refactored 'get_temp_token' function
ME: added 'DEFAULT_TEMP_TOKEN_EXPIRY_TIME' in common.py
ME: refactored calculation of expiry date
ME: added 'expire' action to delete token
ME: updated 'TestConnectViewSet' with tests for temporary token
added 'TempTokenAuthentication' to the default auth classes
ME: added documentation for temporary token functionality
ME: added a test case for expiring a temporary token
Merge pull request #710 from onaio/578-return-temporary-session-token-in-user-endpoint

578 return temporary session token in user endpoint