mediaProperty: skip unnecessary functions for SWIG
mediaProperty: check if access of properties is possible

Throw exception if it's not possible and we can't return any value.
VideoProperties: clean
mediaProperty: rename type MetadatasMap to PropertiesMap

This type is not only used for metadatas, so the new name avoid
confusion.
mediaProperty: rename getDataMap to getPropertiesAsMap
Merge pull request #10 from cchampet/mediaProperty_check_NULL

MediaProperty: check access and rename DataMap