title: NgModule vs Component
body: <p>So I'm learning angular2 now and reading ngbook2 about the modules.
  Modules contain components, but also can import different modules with their public components.</p>
  
  <p>And the question is: What is the scope of the module component (in this meaning scope as parts of an application, not the reach of variables inside). Is module the whole application or just some part like header, containing its components?</p>
  
  <p>What is the typicaly used convention?</p>