Allow LifeViewer on Catagolue to support custom ruletables

The majority of ruletable rules on Catagolue cannot be run by LifeViewer due to there not being a local repository of rule files for LifeViewer to read from. This could be fixed by having rule tables be uploaded to the site somewhere, and then LifeViewer could be pointed to this location to read from.

https://www.conwaylife.com/forums/viewtopic.php?f=3&t=1622&start=1300#p85617

Also, if a rule is detected to be a custom ruletable and not part of any natively-supported LifeViewer rule family, custom colours for the theme should be defined as to match up with the generated preview images.