[!!!][FEATURE] HTTP components for handling requests (Revision 18)

Currently the only way to hook into the request handling process
one has to use a custom RequestHandler (e.g. for CLI requests) or
AOP (e.g. to capture Fluid AJAX-Widget requests).

With this change request handling in Flow is much more modular and
flexible as it allows packages to modify the default request chain
chain by providing or configuring so called HTTP components.

This is not a breaking change strictly speaking as it doesn't
affect the public API. It's marked as such though because
it quite likely breaks Flow applications with custom request
handling.

Change-Id: Iac1bd27cd1f2869e597b696c896633f14703ec40
Resolves: #52064
Releases: master
Revision-Id: 57fcd617d36444697c5c546af164fe4807a69dc2