Enable multi-workers, and faster when loading data by caching data to disk cache
Merge remote-tracking branch 'huoxy/master'
typo
make update_metrics log output for both steps
fixes/cleanups

* remove invoking of building of structured metrics data from
  web app,
  update_metrics does that after downloading the json anyway.
* remove 'metrics' reference and loading of json metrics in
  web app. it's not needed for anything.  this is an optimisation
  but it also fixes a bug, introduced in the local caching commit
   where GE would keep saying
    ```
    Can't load metrics file
    [Errno 2] No such file or directory: 'metrics.json'
    ```
  if it was started without a metrics.json and even after
  update_metrics did everything.
  it also fixes another bug where GE would incorrectly check just
  the json to see if the data was ready, it should check the
  targets and graphs list
cleanup/fix wrt loading the pickle files

* refactor is_data_latest a little to isolate its use of the
  cache mtimes.
* fix GE errorring out when the pickled file wasn't ready yet
remove /refresh_data link, that feature has been removed