first stab at #77 - add basic graphing engine and added a couple of graphs in the dashboard

fixes #70 - shows hosts in error state in the dashboard

fixes #72: allow to define the default puppet server hostname

fixes #57 - add retention rules to expire old reports

added a label for each report

added delete link from report show action

ugly workaround for broken reports, I think I'll refactor the whole reporting database and import as serializing doesnt seem to work that reliably

Destroyed objects did not show up correctly

• created an audit show page
• added auditing for external node parameters
  refs #43

fixes #28 and converts existing helpers to snippets