Fix nbconflux for nbconvert>=6.0

[nayyarv]

Hi, this is related to #45 and #46

I based this off the PR there but ended up fixing the actual issue since I believe the fix didn't quite work as expected since traitlets act a bit oddly if you're not used to them.

I took @makammoun's changes and a fixed it to actually work against a confluence I have access to. I provided the integration test I used, but I couldn't work out how to actually have this work for anyone. It might not be a bad idea to have a nbconflux confluence for vericast so you can run the test in CI.

I have removed the style includes from the confluence templates as this has been deprecated for years now (no more custom style sheets). There were a few minor cleanups too.

You'll probably want to do a new release as 0.7.0 is likely mostly broken for people.

[eric-tramel]

Can confirm, that of the existing forks etc, this is the PR that truly works. Verified the operation of this using API Token keys. There are two limitations, however:

1. MathJaX does not render (Atlassian Cloud as of April 4, 2022 update).
2. Cell syntax highlighting is not set properly. Code cells are rendered as raw text (however, one can a posteriori come back and set the appropriate language, but this seems burdensome for large notebooks).

Would be a great start to getting around the stale nbconvert problems. However, really need maintainers to come back and give some feedback and/or take one of these PRs.

[chblanc]

Can confirm that this fork isn't working properly with nb_convert=6.5.0. The notebook_to_page command fails with the dreaded TraitError: The 'exporter' trait of a ConfluencePreprocessor instance expected a ConfluenceExporter, not the NoneType None that other users have been experiencing.

[ajstewart]

Can confirm that this fork isn't working properly with nb_convert=6.5.0. The notebook_to_page command fails with the dreaded TraitError: The 'exporter' trait of a ConfluencePreprocessor instance expected a ConfluenceExporter, not the NoneType None that other users have been experiencing.

@chblanc and for anyone else reading this, this branch worked for me today with nbconvert==6.5.0 (still with Eric's caveats above). My only issue was downgrading bleach<5.0 as 5.0 changed the way CSS styles are handled and will break nbconflux.

[chblanc]

@ajstewart I stand corrected. It turns out I accidentally installed the wrong branch. I can now confirm that this is working with bleach=4.1.0.

[kristofer-hannesson]

@chblanc or @nayyarv can you please tell me how to correctly install the branch? I've been trying variations of commands but can't get it to work correctly.

[nayyarv]

I just checked out the branch from my repo and used it directly from there. You shouldn't need to install anything.

[kristofer-hannesson]

For anyone who wants a quick way to install the branch from this fork this command worked for me

pip install -e "git+https://github.com/nayyarv/nbconflux.git@varun/fixnbconflux#egg=nbconflux"