HDM should be able to read global hiera data

[tuxmea]

In some environments, the global hiera data is used (/etc/puppetlabs/puppet/hiera.yaml)
HDM should be able to also show global data.

Workflow in HDM:

• select environment
• select node

1. Global data:

HDM now reads the global hiera.yaml file, replaces the facts and finds the yaml files for the node and collects all Hiera keys.
The global hiera.yaml file may be absent. It should only be taken into account if it has a hierarchy key.

2. Environment data:

HDM reads the environment hiera.yaml file, replaces the facts and finds the yaml files for the node and collects all Hiera keys.

3. Select a key

When selecting a Hiera key, HDM should show the global directory/file structure similar to environment data on top of the environment data.
Global data and environment data views are each have a border around to visualize that these are different data sources.

4. Show result

Show result must first parse global data and environment data afterwards.
lookup_options are dealt in the same way as single environment data.

[tuxmea]

related to #243

[tuxmea]

implemented