Backport observeHandle._fetch from shark
Initial backport of wrapTransform from shark
Review of wrapTransform with avital

- move _makeNonreactive into wrapTransform
- Use EJSON.equals for _id comparison
- Return null for nonexistent transforms
- Use isPlainObject for objectness check
- Add unit tests; remove some end-to-end tests

Also, add an EJSON.clone to the recently backported observeHandle._fetch
Merge branch 'shark-backports' into devel