Docsy migration followup items - 2021Q1

[chalin]

Work items in follow up to #479:

• [x] Update README with site cloning instructions now that we have submodules #594
• [ ] Duplicate partial inclusion in head.html and head-end.html #775
  • [ ] HTML head meta elements are duplicated #745
  • [ ] Homepage has empty title/name for opengraph, twitter, and itemprop #744
• [x] Reducing technical debt
  • [x] Create and use a grpc-docsy theme to hold docsy file overrides #669
  • [x] Npm packages: drop bulma -- it isn't used anymore -- refresh other packages #614
  • [x] Drop unused figure.html shortcode #678
  • [x] Drop style.sass since we aren't using bulma anymore #642
  • [x] Config file has dead code from pre-docsy times #655
  • [x] Use assets/scss/_styles_project.scss to include project-specific styling #700
    • [x] SCSS: revert import order of site variables? #668 Fixed via #702
  • [x] SCSS: why redefine $gray-100? #703
• [x] SEO:
  • [x] Google Search Console is reporting lots of errors #600
  • [x] Prevent indexing of the old GitHub-pages site (#599)
  • [x] Allow indexing of API docs published from grpc/grpc (#612)
• [x] Regression:
  • [x] docsy submodule was regressed to May 2020 #603
  • [x] Layout issue with Showcase page #630
  • [x] Footer updates are needed #660
• [ ] Cleanup
  • [ ] Config: revisit meta tags including those for Twitter and Open Graph #657
  • [x] Homepage isn't mobile friendly #689
  • [x] Homepage: fix logo and image sizes, they're too big #696
    • [x] Homepage: docsy & styles cleanup, slight redesign to reduce oversized element sizes #695
• [x] #582
• [ ] #623
• [x] Upgrade to latest docsy version (2021/02) #610

Questions (not addressed in previous points):

• [ ] Use a shared layout for the About, Showcase and Community pages? #667