Monitoring_AlerthistogramController::indexAction(): find out what to fetch w/ the URL params

refs #4474
Add state map Monitoring_AlerthistogramController::$states

refs #4474
Deduplicate incremention of $data[...][$index][1] by using Monitoring_AlerthistogramController::$states

refs #4474
Unify data preparing for Monitoring_AlerthistogramController::createHistogram() in ...::prepareData()

refs #4474
Unify Monitoring_AlerthistogramController::createHistogram() and ...::prepareData()

refs #4474