Code caching and scope when importing libraries

[tlienart]

Consider:

A
```julia:init
using PlotlyJS
```
B
```julia:ex
some example
```

After the first pass, these two blocks will be cached and not re-evaluated. The issue however is that if we kill the server, add a new code block at the end of the document which requires Plotly, and restart the server, that last code block will fail because the initial code cell will not be re-evaluated and the module has been scraped so that it doesn't load PlotlyJS anymore.

The current way around this is to just use @def reeval = true but this is not the elegant option.

Several simple ways of doing things:

1. use reeval=true (already works)
2. add the using statement in every code block with a #hide, this has negligible cost if the library is already loaded and will ensure the issue doesn't arise

Non-simple way of doing things:

• add some form of command to force a cell to always be reevaluated

this however entails that the scope would be stale after that cell and that everything would potentially need to be re-evaluated afterwards, so there's no clear advantage over just reeval = true I would think.

Another (difficult?) but nice way could be to make "permanent" any statement at least for the duration of the session... That would require:

• at the end of a page build find all modules loaded in the current environment, similar to https://stackoverflow.com/questions/25575406/list-of-loaded-imported-packages-in-julia except that doesn't work anymore
• distinguish between using and import
• save those in something persistent related to that page
• when rebuilding that page subsequently, load that.

[tlienart]

Good solution for this should be to put the imports in utils.jl , need to try first as it imports ..Utils, not using.

We could just go over the symbols loaded in Utils and load all those that are modules them in all submodules... (with the same paths so using/import)