Rework hierarchy for processing sections and address draft comment

[robander]

• Move chunking and branch filtering from "DITA map processing" to "DITA processing"
• Change "DITA map processing" to "DITA maps", now that it describes only maps and subject schemes
• Rename map-processing map and topic to reflect new usage
• Rename topic about DITA processing from behaviors.dita to ditaprocessing.dita