Replace metrics 95th percentile with request to create percentiles

Metrics 0.8.0 introduced a feature that allows to request any number of percentiles to be counted on buckets (with a request parameter percentiles=d,d,d..). The JSON changed from top-level 95th to "percentiles" :

if requesting the same 95th percentile.

Adjust the Hawkular UI to request a percentile that's necessary and read it from the new place.