Fix Binary Metadata storage incompatibility between the value and the field (simple vs list)

When a BinaryMetadata is extracted as a single String while being stored in a StringList field, the BinaryMetadataServiceImpl#writeMetadata method fails when calling doc.setPropertyValue, because you can't store a String in a String list.

The same occurs when trying to store a String in a multivalued String field of course.

The type of the field should be detected and the metadata value modified accordingly: Either create an array of one element, or join the values.

Note: The way the values are stored in the metadata can be different in a picture compared to another, for the same metadata, it depends on the tool that created the metadata. This is why, in some pictures, IPTC:Keywords are extracted as a list, and in other picture as just a string with coma separated words.