Restructure mock file

[axelboc]

Follows #1768 and #1770.

Last but not least, I restructure the mock file significantly so it's cleaner and more logical. The mock demo has grown organically since the project's inception and it was becoming a bit messy.

The mock demo not only demonstrates the H5Web viewer interface to end users — it's also used for development, automated testing, and as a form of documentation of supported HDF5, NeXus and NetCDF features for people who write HDF5 files. The goal is neither exhaustiveness nor end-to-end accuracy — it's to find a middle ground between all of these needs.

The main changes are as follows:

• Consistent use of prefixes for grouping and faster scanning (e.g. group_, default_, etc.)
• Fewer abbreviations (complex, boolean)
• Single nexus group at the root
• Same case as underlying NeXus features (e.g. NXdata, SILX_style)

[axelboc]

/approve

[loichuder]

💪