Pre-rendering on shortcut-style catalog routes

[tephenavies]

• Put logic for loading a model from an old id into a function
• Add prerendering on top of shortcut-style catalog routes

What this PR does

Fixes #

This is a description of what I've done in this PR, especially explaining choices made to make the reviewer's job easier. If I don't replace this paragraph with an actual description, my PR will probably be ignored.

Test me

How should reviewers test this? (Hint: If you want to provide a test catalog item, create a Gist of its catalog JSON, add its url and your branch name to this url: http://ci.terria.io/<branch name>/#clean&<raw url of your gist> , and then paste that in the body of this PR)

Checklist

• [ ] There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• [ ] I've updated relevant documentation in doc/.
• [ ] I've updated CHANGES.md with what I changed.
• [ ] I've provided instructions in the PR description on how to test this PR.