add ComponentEntity::unitsCount() to object model
add ComponentEntity::unitsCount() to object model

MichaelClerx/libcellml,hsorby/libcellml,libcellml/buildbot-testing,nickerso/libcellml,cellml/libcellml,hsorby/libcellml,hsorby/libcellml,nickerso/libcellml,nickerso/libcellml,cellml/libcellml,nickerso/libcellml,cellml/libcellml,libcellml/buildbot-testing,MichaelClerx/libcellml,MichaelClerx/libcellml,cellml/libcellml,hsorby/libcellml