redirect-test: use flag-gray.png (not 1px.png)
[refact] RequestProcessor: coding style changes
[refact] separate file for redirection-related stuff
some changes to `_showRedirectNotification`

dieser
some cleanup
add `HttpResponse`, refactoring and fix #351

The `HttpResponse` class has been added.
Some code of `request-processor.redirects.js` has been moved
into that class.