Rename head contributions to root template contributions

The hst headcontribution(s) tags do not have an appropriate name. The contributions from components lower in the page hierarchy to the top level component can be placed there at any point in the template. References to scripts for example do not have to end up in the html head of the page.

Please create new tags hst.rootContribution(s) or hst.rootTemplateContribution(s) and deprecate the old tag.