In order to generate an URL to the personalization frontcontroller, it
was necessary to instantiate the handler (i.e. the object responsible
for actually delivering the personalized content). Thanks to this
refactoring effort only an independant lightweight request URL generator
object needs to be created in order to construct callback URLs for Ajax
and ESI requests. This also eliminates the dependency between the
default request handler and cache-granularity. The request registry was
renamed to request router to better reflect the responsibility of this
class.