move all 'enhanced metrics' stuff in a separate package
bugfix: load as many plugins as possible
refactoring

* add metrics.json related logic to backend
* make metrics filename configurable
* use python script to download the metrics
include latest version of paste
refactoring of targets/graphs generation, async, paste

* use to multi-threaded paste server and python threads
* at application startup, load metrics, and generate
  structured_metrics' targets and graphs (asynchronously)
  the app listens directly and handles cases where the data
  is not available.  this process can take several seconds
  and doing this on every page request was not feasible
  anymore.
* allow refreshing structured_metrics' data through
  webinterface, make update_metrics.py do this after
  downloading new metrics.json
better name for target whose info is all contained in graph title

it is not necessarily the only target in the graph