Add oauth2 grant type "password" bearer token authentication

Backend:
 - install and configure oauth2-server-laravel
 - implement oauth2 grant type "password" flow (check the
   app/config/packages/lucadegasperi/oauth2-server-laravel/oauth2.php
   config file)
 - inject client id and client token only on the client (backend)
   to the request
 - add CLIENT_NAME, CLIENT_ID, CLIENT_SECRET to the config
 - add OAuth2ClientTableSeeder (uses above config vars)
 - AuthController with login, register & getUserId methods
 - improve routes

Frontend:
 - add angular-http-auth for authentication flow
 - ngstorage for storing auth session data
 - add angular-cache for caching Tags & Things
 - ngDialog for login modal
 - add auth services: authSession, authSrvc, authInterceptor
 - add auth controllers: AuthCtrl, AuthLoginCtrl, AuthRegisterCtrl
 - implement cache in Tags & Things services
 - add login & register templates
 - add app wide config file (angular/src/app/config.js)
 - add overrides for ngDialog to bower.json