PlatformHstModel is very confusing since non-platform-webapp hst models are also an instance of PlatformHstModel

I noticed the PlatformHstModel name is very confusing, because it gives the impression we are dealing with the HstModel for the platform webapp. However, this is not the case, because every HstModel instance for every webapp is an PlatformHstModel instance: The only thing with PlatformHstModel, is that you can only cast to PlatformHstModel if you have the platform-api...it is meant to contain some getters which are not needed for the site webapp developers.

To avoid confusing, I will rename PlatformHstModel to InternalHstModel since it contains some internal api methods. This is much less confusing