Update website to clarify Post45 sections

[wang-arthur]

Readers report confusion between the journal and Contemporaries (articles and essays? issues and clusters?).

We should:

• Edit some website text
  • Replace "about" info on the website with info about publications -- move stuff about the collective elsewhere (related: https://github.com/Post45-Journal/Projects/issues/32)
  • Rewrite the footer description of Post45
• Adjust website design
  • Rearrange home page grid into two columns?
  • Use a different color palette or design language for the journal vs. contemporaries?
  • Note somewhere that journal articles are peer reviewed & Contemporaries essays are editor reviewed? This could potentially be bundled with https://github.com/Post45-Journal/Projects/issues/15 (auto-citation generator)