Should parse resources fetched by a fetch cells synchronously

[wlach]

Load this notebook and click "run all":

https://extremely-alpha.iodide.io/notebooks/148/?

Expected:

See a graph in the report view

Actual:

See a console error because it tries to render the graph before all the supported libraries are fully loaded. If I run the fetch cell again (e.g. by clicking run all a second time), it seems to load the libraries successfully.

[wlach]

Talked to @hamilton and apparently this is the way things work right now -- we both load and parse asynchronously, so a resource that depends on another might be loaded in the wrong order (in this case d3 seems to be loaded after metrics-graphics). We should be able to fix this by modifying the fetch cell to parse resources only in the order they are defined, rather than as they are fetched (we can still fetch them async for maximum performance).

[wlach]

Another internal example of this error case: https://definitely-staging.iodide.io/notebooks/210/