generated index.html facade should suppress link to features/ & site.properties for bundle-only sites

The generated index.html facade should not provide a link to features/ subfolder if the site only contains bundles (plugins/ subfolder), since the link is 404'd.

Example sites w/ no features:

http://download.jboss.org/jbosstools/updates/nightly/integration-stack-tests/4.1.kepler/
http://download.jboss.org/jbosstools/updates/nightly/integration-stack-tests/master/

Need to parameterize this bit of XSLT [0]:

[0] https://github.com/jbosstools/jbosstools-maven-plugins/blob/master/tycho-plugins/repository-utils/src/main/resources/xslt/site.xsl#L113-L114

Also, we should probably not generate a site.properties file [1] for sites w/ no features as there's no features to list in the file.

[1] https://github.com/jbosstools/jbosstools-maven-plugins/blob/master/tycho-plugins/repository-utils/src/main/resources/xslt/site.properties.xsl