Ignore text nodes when parsing XMLAnnotation's value

This fixes an error parsing Modulo annotations
(e.g. FLIM-modulo-sample.ome.tiff) in Matlab.
xsd-fu: Add instanceType property to property
xsd-fu: Add isShared and isWeak properties to property
xsd-fu: Move template configuration to language
cpp: Add and use OMEXMLMetadata template
Merge pull request #854 from rleigh-dundee/cpp-omexmlmetadata

cpp: Add OMEXMLMetadata template
Merge pull request #853 from melissalinkert/xmlannotation-parsing

Ignore text nodes when parsing XMLAnnotation's value