138 assign meta data to each data point numbering of experiments

This PR introduces a meta-data block to each data row as specified in #138

Open tasks to be completed before merging

[x] Make sure enabled/disabled flag is respected where needed
[x] Make sure export to CSV sorts lines by index (We don't do this)
[x] Introduce row ID (rename index)
[x] In CSV import/export handle optional meta data fields only present on some entries
[x] Clean up types
[x] Clean up convert method (readability)
[x] Expose meta data in editor/list (minimal, defer proper solution to separate task)
[x] Clean up commit history