modules: add admin stats module.

Work in progress. Currently only charts a snapshot in time,
so no real time updates... Also more work on the graphs themselves
are needed.

Still missing (line) graphs for request counts for the different
time spans. But that is not really effectful until there's live
update of the graph data, appending the latest statistics.
core: all acl checks has to pass.
(cherry picked from commit f1930b97f79d0074493a6955ef92455e161c6afc)
mod_admin_stats: reworking the histogram charts.
mod_admin_stats: working on transitions.. loading smooth now. :)
mod_admin_stats: fix fill-opacity after loading
mod_admin_stats: live updates of histogram charts.

Work in progress. Currently updates on the push of a button.
Also removed the now unused nvd3 lib.
mod_admin_stats: cleanup.

Got rid of javascript variables. Use wire's to hook everything up.
Renamed the request/response notify/event pair to 'update_metrics'
and 'new_metrics' resp.
mod_admin_stats: major refactoring, introducing chart factories.

Also moved somewhat generic parts into z_charts.js for future break out
into a generic chart module.
mod_admin_stats: begun work on line charts...
mod_admin_stats: Line charts in place, as well as live updates.
mod_admin_stats: some cleanup + new text labels and start/stop buttons.
mod_admin_stats: convert mean values to milliseconds.
mod_admin_stats: add five, fifteen and day line series to the charts.
mod_admin_stats: fix line chart to last 5 minutes.
mod_admin_stats: fix clip path.
Merge pull request #2 from kaos/z_stats

modules: add admin stats module.