Unit tests for data module

[ns-rse]

Develop unit tests for the data module (see #80 for overview).

Specific modules within data are...

• data/demo_data.py
• data/HOA_tools_cec2.py
• data/scene_builder_cec1.py
• data/scene_render_cec1.py
• data/scene_render_cec2.py
• data/utils.py Introducing tests for clarity.data.utils module #88