Add seamless learning docs

[phrdang]

• Update top level page order
• Add seamless learning index
• Add seamless learning subpages for relevant projects

[pancakereport]

Data Science Curriculum Guide is not a Seamless Learning project so we shouldn't take credit for it. But I definitely think that it should be featured and referenced heavily.

Also, Benji and Celina's work on the section tool (paid for by Seamless Learning) should be featured. Open source repo here: https://github.com/Cal-CS-61A-Staff/sections

[phrdang]

Thanks for the feedback, I moved the DS curriculum guide into "quick links" under a new section called "Course Software." I also moved the entire Otter section under Course Software.

Also added the sections tool to Seamless Learning.

In order to have arbitrarily nested child pages, I also bumped just-the-docs to v0.10.0 which also deprecates the has_children front matter field, so I removed that everywhere as well.

[pancakereport]

we can always make more changes later, lol