Draft for 3.7, 3.8 or 4.x ? ...

Rationale

• AggregationState is a very rough 1:1 copy of Resource and Aggregator, and improving this area would take templating improvements of 3.7 even further.
• AggregationState as a class name isn't very satisfying.
• Resource is still in use, and despite being deprecated, I have the feeling AggregationState hasn't been adopted yet.
• Resource has a couple of features that haven't been moved to AggregationState: the preview mode being the useful one (I suspect all other methods could or should be removed)

Points to discuss

• RenderingState ? Would hold "currentNode" and friends.
• Are properties like file, form, etc really relevant ?
• Properties related to the admininterface, like "preview" should move to a different object. It should be clearer that RenderingState (or other name) holds information related to the actual content being rendered, not the edit bar or other artifacts.

Additionally, if the "preview" flag wasn't stored in the session but simply passed in the url, it might help when rendering resources from the repository like css (see MAGNOLIA-2393@jira)