* puppetboard/app.py: Adding Radiator view
Part 2 of https://github.com/voxpupuli/puppetboard/issues/70
This is a refactoring of the changes in https://github.com/voxpupuli/puppetboard/pull/100.
Adds a simple Heads-Up Display of the last run statuses of managed nodes,
either environment filtered or not.
* puppetboard/app.py: Fixing environment filters and metric strings.
* The names of the population metrics have changes in PuppetDB 4.0, the initial
commit used the metric names from PuppetDB 2.x.
* The main nodes query did not include a query string to filter on environments.
