Implementing new pypuppetdb.QueryBuilder (#251)

* puppetboard/app.py: Implementing and utilizing the new PyPuppetDB QueryBuilder

This fixes https://github.com/voxpupuli/puppetboard/issues/239

Replacing all the directly declared query strings with various objects
from the pypuppetdb.QueryBuilder sub-module. Using this Object-Oriented
functionality it is programmatically safer to construct large, complex
queries.

* puppetboard/app.py: Simplifying the environment logic in `node()`

The query in this function will now always be an `AndOperator()` object.
If a specific environment is queried then that constraint is added.

The resulting query difference will be:

env == 'production'

`["and",["=", "environment", "production"],["=", "certname", "puppet01.hammertime.local"]]`

env == '*'

`["and",["=", "certname", "puppet01.hammertime.local"]]`

* puppetboard/app.py: Minor code simplification for more accurate results.

In index() adding the configured OVERVIEW_FILTER query after adding the previous
constraints to num_nodes_query
In inventory() wrapping fact_query in an AndOperator() regardless of environment.
This update makes it more common with other endpoints that only add environment
constraints if an environment is selected.

* requirements.txt: Bumping the pypuppetdb version requirement

* requirements.txt: Bumping pypuppetdb version to new requirement.

* puppetboard/app.py: Fixing module load error.

setup.py

@@ -32,7 +32,7 @@ setup(
         "Flask >= 0.10.1",
         "Flask-WTF >= 0.9.4, <= 0.9.5",
         "WTForms < 2.0",
-        "pypuppetdb >= 0.2.1, < 0.3.0",
+        "pypuppetdb >= 0.3.0, < 0.4.0",
         ],
     keywords="puppet puppetdb puppetboard",
     classifiers=[