Analyse and interpret BAILII links

[jcranch]

Bailii's files contain lots of links. We should read them and process them:

• if it is a link to another judgment on bailii, we should try to promote it to a link the relevant judgmental page (without duplicating the efforts of the crossreference linker);
• if it is a link to some piece of locally stored legislation, we should try to promote it to a link to our preferred relevant legislation page;
• if it is something else, it should probably be preserved.