Regression : Different hst:sites cannot reuse one and the same hst:configuration any more

It used to be possible to have a hst:site that reused the exact same hst configuration but only had a different content tree.

The only way to support this valid setup is to support the hst:configurationpath on a hst:site to explicitly point to some hst:configuration node. So, we cannot deprecate the hst:configurationpath

Also, we now need to make sure that if two sites point to the same hst:configurationpath. we need to bump the hst:version's for both when publishing the configuration