LIBKML: add support for creating BalloonStyle elements

git-svn-id: https://svn.osgeo.org/gdal/trunk@27059 f0d54148-0727-0410-94bb-9a71ac55c965
LIBKML: make sure atom namespace is written in doc.kml of .kmz if necessary

git-svn-id: https://svn.osgeo.org/gdal/trunk@27060 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx