functionality to add occurence and measurement level information

[fdschneider]

feeding in a data table to link to measurementID or occurenceID or locationID (for georeferencing exploratories data).

[fdschneider]

This requires a merge() method for traitdata. The y argument is a defined data.table containing standard columns and the by argument would be the unique Identifier, e.g. measurementID, occurrenceID.

For the different types of data, a different behaviour is neccessary:

• traitID can be used to add own standard values, would be used to acheive traitID standardization? prompts standardize.traits() ?? some redundancy in logic!
• taxonID, would be used if merging own Std entries. would overwrite entries created by standardize.taxonomy()
• measurement ID should overwrite existing entries, e.g. traitUnit
• occurrenceID can overwrite existing entries of occurrence extension
• datasetID can be used to add metadata
• eventID, locationID have overlapping scope