Oldkea linkfixes

This is a collection of updates to links to the oldkea.isc.org wiki pages. Where we were linking to a design or requirements document, I migrated the document, or found it already migrated, in the new wiki on gitlab.isc.org. Where the link was to a specific Trac ticket on oldkea.isc.org, I left it as is.

There are one or two places where I thought there was no good reason for an external link and I removed it, but mostly I resisted the temptation to do that.