[minor] CS fixes
Added Psr\HttpMessage\MessageInterface and Psr\HttpMessage\RequestInterface implementations and tests
Moved Request object into a subnamespace for message related classes
Moved HttpMessage into message namespace
Moved Response class into message namespace
[minor] CS: use tabs for indentation
Namespace fixes
Created an abstraction for building MessageInterface objects which is used by the Router to retrieve the messages it needs.
Added a MessageBuilder implementation that builds RequestInterface messages for the currently processing request in a web context
Update the Router to use default message builder that builds messages for the currently processing request