Enhance node status feature in overview and nodes

This commit uses the new parameter with_status from nedap/pypuppetdb#18

Node status is now shown as text with the additional information of
failed/succeded events, unreported time

The statistics on Overview now show the *number of nodes*
that have status failed/changed/unreported

![screenshot_overview](https://f.cloud.github.com/assets/3404133/1472140/156930e4-45fb-11e3-8771-322ed1cf0596.jpg)