Backport : Support parameters of mount (by hst:parameternames and hst:parametervalues) to be used in sitemapitem/component

This improvement idea was discussed in the mailinglist. [1]
Currently, the parameters in mount by hst:parameternames/hst:parametervalues are not available in sitemapitem and component. And, it is not possible to use the parameters in mount for hst:relativecontentpath in sitemap item, either. e.g., 'hst:relativecontentpath' = '${defaultnewspath}', 'hst:relativecontentpath' = 'nouvell_${region}', etc.
It would be really useful and convenient for developers if kind of global parameters in mount could be used in each sitemapitem or component.

[1] http://hippo.2275632.n2.nabble.com/Hst-parameter-definition-inheritance-from-mount-td7579860.html