Also fix a couple of bugs around this: for example, if you loaded a Jupyter notebook and then switched to "Source" view, blame would incorrectly fail to activate because the original rendering of the "stage" used an asynchronous engine so willRenderRef() wasn't called to populate blame.
- Viewed a source file, toggled blame off/on, reloaded page to see state stick in URL.
- Viewed a Jupyter notebook, toggled to "Source" view, saw blame.
- Viewed stuff in Files (no blame UI options).
- Tried to do some invalid stuff like toggle blame on a non-blame engine (options disable properly).