o.c.product: fix introDescription properties in plugin.xml
o.c.product: fix introDescription properties in plugin.xml

The pages included in the CS-Studio product are defined in
plugin_customization.ini, in org.csstudio.product.configuration.feature:

  org.eclipse.ui.intro.universal/org.csstudio.product.product_INTRO_ROOT_PAGES=firststeps,tutorials,whatsnew

so there should be an "introDescription-XXX" property for each of those.

"introDescription" (without a suffix) isn't a valid option, according to:

  http://help.eclipse.org/luna/index.jsp?topic=%2Forg.eclipse.platform.doc.isv%2Fguide%2Fua_intro_universal_contributing.htm

ControlSystemStudio/cs-studio,ControlSystemStudio/cs-studio,ControlSystemStudio/cs-studio,ControlSystemStudio/cs-studio,ControlSystemStudio/cs-studio,ControlSystemStudio/cs-studio