Add basic support for node status by using the most recent report

The following frontend features are implemented
- Number of failures, successes, noops/skips in overview
- Show latest reports with 1 or more events in overview
- Direct links to latest Report
- Number and types of events in nodes list
fix for required branch of pypuppetdb with new api support
show list of nodes without report for x hours in overview

- the amount of hours is defined as `UNRESPONSIVE_HOURS` in default_settings.py
- small status layout improvement in nodes list
- latest report button in nodes list
- nedap/pypuppetdb repo as requirement ( new api was merged nedap/pypuppetdb#17 )
remove duplicate mean_command_time
Merge pull request #22 from digitalmediacenter/feature-status

Add basic support for node status by using the most recent report

Closes #5 #15