Default ACL text should show all features

We haven't updated our default ACL text in a long time. We should make sure it shows or references all the interesting features:
- [ ] Hostnames and subnets (both as source and as destination)
- [ ] autogroup:same-user (or whatever we end up calling it)
- [ ] role:user and role:admin (or whatever the new names are)
- [ ] ACL tags and TagOwners
- [ ] Users as destinations, not just sources
- [ ] Tests
- [ ] Route AutoApprovers
- [x] SSH

It would be okay to link to KB articles etc from the comments to explain the various features.

Updating the default text is generally harmless since the text won't actually save in the database unless it's modified.

Note that the default/example ACLs must always have a global "allow everything" rule at the bottom, since the default is to allow everything.