BinaryMetadata - Add a parameter to make it optionally read-only

By default, the MetadaMapping is a bidirectional: Values are read from the blob and stored in fields, and if the value of a mapped field is modified and the document is saved, the value is then written into the blob. This behavior is sometimes not desirable, so we added a new property to the extension point: readonly . If the value is readonly="true" , then modifying a field will not modify the binary. Default value is « false » to preserve compatibility with existing configurations. Example: <extension target= "org.nuxeo.binary.metadata" point= "metadataMappings" > <!-- has the readOnly flag set to true, will not write to blob --> <metadataMapping id= "PDF-ReadOnly" processor= "exifTool" blobXPath= "file:content" ignorePrefix= "false" readOnly= "true" > <metadata name= "PDF:Language" xpath= "dc:title" /> </metadataMapping> <!-- No readOnly flag: Plugin can write to blob --> <metadataMapping id= "PDF-ReadWrite" processor= "exifTool" blobXPath= "file:content" ignorePrefix= "false" > <metadata name= "PDF:Producer" xpath= "dc:source" /> </metadataMapping> </extension>