fix: refactored lib folder patterns surrounding posts + showcases

[bodom0015]

Problem

There is quite a bit of copy-pasted code between the Posts + Showcases

We would like a better pattern for adding new categories to avoid copy-pasting as much in the future

Redo of #312

Fixes #302

Approach

• fix: restructured PostLayout + Showcase into src/components/Layout
• fix: refactor PostLayout + ShowcaseLayout slightly to more easily include new categories in the future (e.g. Guides, see #317)
• fix: refactor lib folder to cut down on some of the copy-pasted bits - maintain separate implementations for these resources
  • NOTE: After cleaning up this code, the Showcases are no longer sorted by Date - this will be fixed by #303

How to Test

1. Navigate to the list of "Project News" (PostList / PostItem): http://localhost:3000/news
   • You should see no changes compared to production: https://sdohplace.org/news
2. Choose an article (Layout -> PostLayout): http://localhost:3000/news/finding-healthy-food-connecticut
   • You should see no changes compared to production: https://sdohplace.org/news/finding-healthy-food-connecticut
   • NOTE: Images appear differently here, but these are not style changes - production appears to use different screenshot paths than dev
   • NOTE: Copyright symbol (at the bottom) has moved to the left a few pixels - I could not track down why, but this is barely noticeable
3. Navigate to the list of "Fellow Showcases" (ShowcaseList / ShowcaseItem): http://localhost:3000/showcase
   • You should see no changes compared to production: https://sdohplace.org/showcase
   • NOTE: Images appear differently here, but these are not style changes - production appears to use different screenshot paths than dev
4. Choose a showcase (Layout -> ShowcaseLayout): http://localhost:3000/showcase/windham-willmantic-conn-food-access-map
   • You should see no changes compared to production: https://sdohplace.org/showcase/windham-willmantic-conn-food-access-map
   • NOTE: Images appear differently here, but these are not style changes - production appears to use different screenshot paths than dev
   • NOTE: Copyright symbol (at the bottom) has moved to the left a few pixels - I could not track down why, but this is barely noticeable

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[bodom0015]

I'm noticing that the font-size of the page header has changed somewhere... checking to see if I may have lost a bit of needed CSS along the way 🤔

[bodom0015]

@mradamcox I think I've fixed all the styling discrepancies here :+1: sorry for the additional delay on this - I completely agree that we don't want any styling changes here as a part of this merge

Regarding the title, it looks like this is set incorrectly in config.json (contains "News"). Should I go ahead and correct that here? I don't think this is a regression if the bug currently exists on the production site, but maybe I'm missing some context?