[SPA++] SPA mount should render only the root component

An SPA mount will typically be something like this:

+ hst:root        [hst:mount]
     - hst:namedpipeline = SpaSitePipeline
    + resourceapi    [hst:mount]
       - hst:namedpipeline = PageModelPipeline

Now, the hst:root mount and the 'resourceapi' will point to the same hst:configuration node. However, when the hst:root is hit, only the root component needs to be rendered that serve the html for the SPA, and when the resourceapi mount is hit, all the components need to be rendered.