Fix #28 as post process at g2svg

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`).