introducing dependency injection
Merge branch 'master' into feature/di

Conflicts:
	app.js
	routes.js
	src/controllers/UserController.js
	src/service/UserService.js
modify tests to use injector
Remove singletone implementation in UserService

Injector already provides it implicitly.
Add dependency injector documentation to README.md
Merge pull request #27 from clevertech/feature/di

Introducing dependency injection