Remove embedded external plugins/features from the Papyrus features

We should not embed external plugins/features into our features. Current Papyrus embed (at least) these components in its features:

• "org.eclipse.nebula.cwt.feature"
• "org.eclipse.nebula.widgets.nattable.core.feature"
• "org.eclipse.nebula.widgets.nattable.extension.glazedlists.feature"
• "org.eclipse.nebula.widgets.nattable.extension.nebula.feature"
• "org.eclipse.nebula.widgets.richtext"
• "ca.odell.glazedlists"
• "com.google.guava"
• "com.google.gson"
• "org.apache.logging.log4j"

We will declare them as 'required' but we won't provide them. We will declare their update site in our category.xml file