Update version constraint message
Create development and production front ends
Refactor the Application

 - Indent with 4 spaces
 - Add run method instead of executing everything in constructor
 - Inject Symfony HttpFoundation Request into Application
 - Replace SERVER superglobal queries with geting values from the Request object
 - Create a Symfony HttpFoundation Response and send headers from it
 - Create a small dependency injection container (to be replaced with
   Pimple or Symfony DI)
Merge branch 'develop'