Merge pull request #22 from picturae/17121

Fix skos namespace set. refs #17121
Merge remote-tracking branch 'upstream/master'
Add XML declaration to export template.
Create empty data storage directories.
Update README for additional directories requiring web server write access.
Make import to update concepts if notation matches. refs #17315
Merge pull request #23 from picturae/17315

Make import to update concepts if notation matches. refs #17315
Merge pull request #34 from picturae/17315

Make import to update concepts if notation matches. refs #17315
Merge pull request #33 from europeana/create-data-storage-dirs

Add empty data storage directories
Merge pull request #32 from europeana/xml-export-xml-declaration

Add XML declaration to export template.
Refactor import method. Implement concept schemes purge option. refs #17295
Merge pull request #35 from picturae/17295

Refactor import method. Implement concept schemes purge option. refs #17295
Add additional check for unique notation. refs #17544
Merge pull request #36 from picturae/17544

Add additional check for unique notation. refs #17544
Resolve upstream merge conflicts.