Clustering analog add use trigger ts

• Adding the option to use trigger time stamps instead of seed time stamp as cluster time stamp in ClusteringAnalog. Similar as implemented in ClusteringSpatial. This is useful in some cases where events are build based on trigger numbers although time stamps are available.
• Added corresponding entry in documentation.
• Tested enabled myself.
• @naomi tested disabled (default).
• Fixed formulation in the include_corners description.