Change searches to use stats instead of top

Change puppet_changes_by_* searches to use 'stats count by xxx' instead
of 'top xxx', as the latter does not play well with drill-down. As a
result, drill-down now works in the statistics view.
Reworked statistics view

* Chart & table are now in the same panel, which takes up less
  horizontal space and makes the relationship more obvious.

* Charts changed from FlashChart to JSChart.

* Chart, table row and all results drill-downs now work as expected.

* Charts and tables are wrapped in NullModules for layout, which makes
  the relationship clearer.