New EntryGroup type for related but not composite data

[AlexDo1]

Related data like wind speed and wind direction measured at the same location could be grouped into an EntryGroup.

Currently, the following EntryGroup types are available:

• "Project": "A Project groups datasets into a lager collection of datasets that have been collected or used in the same Campaign."
• "Composite": "A composite dataset groups a number of datasets that are inseparable."
• "Split dataset": "A split dataset groups a number of identical datasets that have to be split e.g. in case of different time scale resolution."
• "Label": "A Label groups different datasets into a larger collection of datasets, that are now a composite, but i.e. collected at the same site."

The Label type could be an already implemented appropriate type, but only if the description contains a typo. I think it should be "not a composite" instead of "now".

[AlexDo1]

This could also be useful for @MarcusStrobl, as it would make it easier to find related data that is often needed together for data visualization (like wind roses).