Crusade showdown delay timer [merge after prev. PR]

This PR is a branch off the 'removal of randomized rulers' PR.  Merge that one first.  I've not tried doing separate, open PRs before, so if you run into any merge trouble (it'd just be over the ChangeLog), I'm assuming whatever GitHub presents you as a merge tool will work (whereas if it were event files, a GitHub GUI merge tool might fuck-up the file encoding).

- Crusades will no longer almost instantly start after the scenario but require ~10-20 years before firing.  This matters a lot, for a variety of reasons, in any post-1103 start.