Resolve "Improved GUI search tests"

Closes #748 (closed)

@mscheidg: Could you take a look and see that my overall approach is reasonable. Especially I'd like some comments on:

• I had to somehow formalize the test configuration, and for now, I did it by creating a config file at nomad-FAIR/nomad-test.yaml. This configuration is loaded when node.js is instantiating the test states and should also be used when serving the application for test usage (nomad admin run appworker). Is this approach OK in your opinion? Btw: I had to put the config file in the repository root folder, because otherwise the volume access is not working.
• Do you think the current configuration in nomad-FAIR/nomad-test.yaml is distinct enough so that it does not interfere with other instances?
• Can you take a look at some of the snapshot files (e.g. gui/tests/data/search/min_max_aggregation_n_elements.json) and see if the format is OK?