Dmedia 13.12

Note: Dmedia has NOT earned its "production ready" wings yet, so please treat this release with the usual caution. Test Dmedia, give us feedback, but don't trust your data to it... yet.

Changes include:

* The Dmedia service is now managed by Upstart: although there might be a few issues we still need to sort out, overall this is a big step forward in reliability; some things that developers and expert users should be aware of:

  - the dmedia-service log file is now ~/.cache/upstart/dmedia.log

  - to stop dmedia-service: `stop dmedia`

  - to start dmedia-service: `start dmedia`

  - to restart dmedia-service: `restart dmedia`

  - to see if dmedia-service is running: `status dmedia`

* Clean up imports so dmedia-service doesn't do any unnecessary module imports, which has considerably reduced the baseline memory footprint of dmedia-service

* Clean up and simplify how Core saves its state to the dmedia/machine doc (to reflect currently connected FileStore and currently visible peers)

* Remove now unused file/fragile CouchDB view and its unit test

* Replace TaskQueue, TaskManager with new TaskPool, TaskMaster, which brings considerable improvements:

  - Vigilance is now automatically restarted should it crash (as before, Vigilance is still forced to restart at a regular interval, currently every 23 minutes)

  - the scan/relink/verify is now done in parallel for all connected FileStore, meaning Dmedia will converge far more quickly when a large number of copies need to be verified across several drives

* Add new `dmedia-cli Tasks` command to see the status of the active background tasks

* Improve performance when verifying a large number of small files by retrieved 17 docs at a time (although note they are still saved one at a time)

* Switch (almost) all the scripts from `optparse` to `argparse`, and added basic sanity check unit tests for these scripts