Create draft for first NeXuS application for EM

• Take Christophs JSON STEM example, check how every point maps to NeXuS class, arrange into hierarchy
• Take Adrien and Cecile's mind map example, check how every point maps to NeXuS class
• Take Sherjeel/Benedikt Haas JSON example for Nion microscope instrument control dump data, check how every point maps to NeXuS class, arrange into hierarcy
• Create hierarchical file yaml
• Identify default plottable quantities