Fix #28 as post process at g2svg

The idea is to leave the graphs as they are, and only fix #28 when we render:

1. If there are timestaps, the later cable refers to the earlier cable
2. Missing cables should be reference and not referrer
   (regardless of the date we've guessed for them)

I hope this logic makes sense.

Note that there are missing cables like [06STATE190832](https://dubiousdod.org/uri/URI:DIR2-RO:r7xnodn7et6d3ex44p77qk4eka:nvca4ivhhm2an3eafzpg7wpppy7osgyxvngng5uriqjv2qkcag6a/Latest/static/c2g/5b26861bfa2dc3e06ebf74f67a0a85ea.graphml.html#06STATE190832) with an approximate date later than those of the cables referring to them. This is why I wrote it so that missing trumps date.

On the other hand - the algorithm for guessing the date of a missing cable should take into account that it should be earlier than all cables referring to it (unlike `06STATE190832`).