Remove unused labels from messages.properties files

Some labels are not used anymore in the application and should be removed from messages.properties files.
Below is a list of labels I think are not used anymore. Please check before removing them.

• label.files.files.filename
• label.files.files.file
• label.dublincore.relations
• label.login.IEExtension
• label.login.firefoxExtension
• label.login.liveEdit
• label.login.forums
• label.login.language
• label.syndication.rss
• label.syndication.atom
• label.login.goFurther
• label.login.improveYourExperience
• action.new.file
• command.mass_edition.addworklist
• label.login.forums
• command.create.workspace.wizard
• action.admin.center
• label.picture.byline
• tab.elastic.query
• label.picture.headline
• label.picture.slugline
• label.picture.subheadline
• label.picture.typage
• label.widget.iptc_info.headline
• label.iptc.by_line_title
• label.versioning.createSnapshot