Changes

include induced edges in subgraph link for ref pages.
This matches the actual graph generation rules for the static subgraph.
 (commit: 80d6bbe)

Implement a less aggressive mode for heuristic dating supplementation.
Dating supplementation works on the assumption that when a source states 
a witness has not been created after a certain date but says nothing 
about the earliest possible moment it still suggests a certain closeness 
of the creation date to that terminus ante quem (and the same is valid 
the other way around).
The behaviour can be configured using the new option half_interval_mode:
- always: whenever a source gives only one end of the possible dating
 interval, supplement the other interval limit
- light: when we have only sources about one interval limit but none
 about the other, take the strongest source and infer the other interval
 from that.
The length of the artificial interval can be configured by
half_interval_correction.
 (commit: 9bb2b03)