jupyter notebook format conversion

[moravveji]

This PR elaborates on a newly added feature for converting jupyter notebooks from .ipynb to other interesting formats, specially to PDF which requires an extra step.

[w-lampaert]

Perhaps this would be better in a next PR, but I do feel like this is a good time to bring up again that the Ondemand page is getting quite lengthy. We're also adding more and more things to each of the apps, and only including more apps, so perhaps a page per app (or a separate app page) would be something to consider?

[smoors]

Perhaps this would be better in a next PR, but I do feel like this is a good time to bring up again that the Ondemand page is getting quite lengthy. We're also adding more and more things to each of the apps, and only including more apps, so perhaps a page per app (or a separate app page) would be something to consider?

indeed, that's what i did in #449
please let me know if you have any remarks?

[lexming]

Due to the changes in #452, this file has moved to source/compute/portal/ondemand.rst.