0.10.2 importer fix

[Severino]

Fixed

• Fixed Date Range importFrom to return a JSON string
• Fixed Date Range component in the frontend

Changed

• Added tests to ApiDataImporterTest to check if the same columns can be used in multiple attributes
• Added in testing data an attribute ('Aufbewahrung' [string]) to the entity type 'Fundstelle'
• Changed the row error from just sending the column name to also send the column value
• Dropdowns in the Data Importer are now sorted alphabetically, both the order of the attribute mappings and the option lists inside the dropdowns
• The ErrorList component of the Data Importer in the Frontend now preserves text inside {{...}}