Package in swestore_staging dir. Add functions to get and set storage status

Hej,

This pull request is part of the automatic cleaning functionality. It is not finished but all these functions work, so I think that is more convinient to review it in parts. This PR includes:

 * ```pm archive swestore --package-run --check-finished``` packages a run located in swestore_staging (described in pm.conf) if it is finished (RTAComplete.txt) exists. The ```--check-finished``` option can be omitted and will package the run anyways.

* added functions ```get_storage_status``` and ```set_storage_status``` to the class ```FlowcellRunMetricsConnection```. Those are helper functions for the automatic cleanup functionality.

P.S: Sorry for the spaces and newlines mess... I had an argument with my editor :-/