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

![puppetboard-status](https://f.cloud.github.com/assets/3404133/1418980/8050fef4-3fc1-11e3-8315-2ea9db1cb4c3.png)

Overview:

- display counter for failed/succeeded nodes on Overview page
- show list of latest reports with events on Overview page
- show list of hosts without a Report since x hours
- add direct links to latest Report

Nodes List:

- display number and type of events on Nodes page
- add direct links to latest Report

This may refer to nedap/puppetboard#15 and nedap/puppetboard#5