Fix documentation mention of Request::instance

Various place in guide and php comments were mentionning
Request::instance() to be used. I replaced it either by
Request::factory() or something more appropriate.
inject routes to avoid conflict with application's routes
Merge pull request #458 from enov/bugfix/3967/inject-route-in-request-test

Fixes #3967: inject routes in request tests to avoid conflict with application's routes
Merge pull request #455 from Asenar/3.2/develop

Fix documentation mention of Request::instance

refs #4820