Adds a new abstract base class QgsMetadataValidator for validating
metadata against standard schemas.
Initially only QgsNativeMetadataValidator for validating against
the native QGIS metadata schema is implemented.
In future this could be extended with Dublin Core, ISO 19115
validators, etc...
QgsLayerMetadata handles storage and management of the metadata
for a QgsMapLayer. This class is an internal QGIS format with a common
metadata structure, which allows for code to access the metadata properties for
layers in a uniform way.
The metadata store is designed to be compatible with the Dublin Core metadata
specifications, and will be expanded to allow compatibility with ISO specifications
in future releases. However, the QGIS internal schema does not represent a superset
of all existing metadata schemas and accordingly conversion from specific
metadata formats to QgsLayerMetadata may result in a loss of information.
This class is designed to follow the specifications detailed in
the schema definition available at resources/qgis-resource-metadata.xsd
within the QGIS source code.
