* make variable naming reflect ASEnvironmentTraitCollection vs ASTraitCollection
* move trait propagation to cell allocation instead of via a nested block
* move trait propagation when setting a displaynode's supernode instead of when adding a subnode
* fixed misspelling of "colection"
- _populateFromDataSourceWithSectionIndexSet doesn't accept a mutanle array but allocate one itself.
- Remove _populateFromEntireDataSourceWithMutableContexts.
- ASIndexedNodeContext executes its block, nil out the block and return the result.
- It is a container object that holds enough information to construct and measure a cell node
- All information is gathered on main thread. This allows ASDataController to capture the correct state of its data source before going to background.
