Add PROTEUS module diagram

[stuitje]

Description

This PR updates the proteus-framework.md page with the new PROTEUS schematic via JSDeliver. For the light+dark switch and correct size, a new stylesheet is added; this is extra.css. The old extra.css has been renamed to proteus_theme.css since this configures the general theme of the website. footnotes.css has been added for citations in this style [1] instead of superscript style. For this reason, all citations ([^cite (...)]) have a space added, so that it renders like [1] and not like[1]. This means many files are changed but all with the same change.

It also updates the Atmodeller+FastChem links. PLATON has been removed.

Validation of changes

Built the site locally on safari, firefox and chrome.

Checklist

• I have followed the contributing guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my code
• My changes generate no new warnings or errors
• I have checked that the tests still pass on my computer
• I have updated the docs, as appropriate
• I have added tests for these changes, as appropriate
• I have checked that all dependencies have been updated, as required

[nichollsh]

Great! Builds fine on my laptop with firefox. Thanks for meticulously correcting all the citations so that they format correctly.

[stuitje]

Great! Builds fine on my laptop with firefox. Thanks for meticulously correcting all the citations so that they format correctly.

Thanks! I should probably also check the other module docs ....