docs: make references to Seedcase software/products more uniform

[martonvago]

Description

This PR attempts to make references to Seedcase more uniform. I've tried to stick to the following guidelines:

• "the Seedcase Project": always capital S and P; use to refer to the project as a whole (including underpinning ideas)
• Bare use of "Seedcase": only allow when it refers to the project as a whole in very general terms
• "Seedcase products" / "Seedcase software" / "Seedcase software products": use to refer to the software deliverables of the project; choose best fit based on context
• "the Seedcase framework": use to refer to the collection of software deliverables that work together to implement the core functionalities; use in older documentation to shift the meaning away from a single product without rewriting large chunks of text that will probably change significantly anyway
• "Data Resource": always capital D and R; use to refer to the data layer in the framework and its contents

I've also formatted the files I touched, so there are some whitespace and markdown changes. These are a bit more numerous than I was expecting, and they actually make these reviews super annoying to do -- sorry about that!

In general, these changes are pretty subjective and can be controversial, so feel free to be critical.

Related Issues: https://github.com/seedcase-project/design/issues/21

Testing

• [ ] Yes
• [x] No, not needed (give a reason below)
• [ ] No, I need help writing them

Tested in the browser.

Reviewer Focus

This PR only needs a quick review.

Checklist

For general documentation:

• [x] Spell-check
  • [ ] US
  • [ ] UK
• [x] Did the page(s) preview correctly on your machine without breaking
• [x] New category words (keywords) (if any) added to the code snippet file

[martonvago]

I know I've updated some somewhat outdated sections too, but it was easier to do everything all at once. The diagrams I didn't touch though.