POC: WIP: Redesign landing page of PyGMT website

[yvonnefroehlich]

Description of proposed changes

Currently trying out different ideas and approaches regarding improving the PyGMT website landing page. Seeing / experimenting how different layouts would look like.

Major Tasks and changes

• Use cards on landing page, layout 2 columns 3 rows
• Reorder sidebar
• Add new section Project Overview
  • Why PyGMT?
    • Project Goals <- From README
    • Background <- From Getting Started/Overview
    • Support <- From README (maybe rename to Funding)
    • Related Projects <- From README
  • PyGMT Ecosystem <- From Technical Reference
  • Citing PyGMT with G^3 paper and Zenodo BibTex <- From README
  • Conference Presentations <- From Getting Started/Overview
• Add PyGMT logo on landing page via Sphinx markdown instead of html
• Links within documentation: latest or dev? In the README we use latest. This is not optimal for the docs as dev links to latest of the linked doc page not dev.

Make things look nice

• Background color of cards
• Centering of text on landing page
• Vertical space between PyGMT logo and text on lading page
• Rename section Getting Help and Contributing to Getting Help where???
• Add icons

Resourecs:

• https://sphinx-design.readthedocs.io/en/latest/cards.html
• https://sphinx-design.readthedocs.io/en/latest/css_variables.html
• https://sphinx-design.readthedocs.io/en/rtd-theme/grids.html
• https://sphinx-design.readthedocs.io/en/rtd-theme/badges_buttons.html#octicon-icons
• https://sphinx-design.readthedocs.io/en/rtd-theme/css_classes.html

Preview:

• Landing page: https://pygmt-dev--4762.org.readthedocs.build/en/4762/
• Project Overview/Why PyGMT?: https://pygmt-dev--4762.org.readthedocs.build/en/4762/overview.html
• Project Overview/Citing: https://pygmt-dev--4762.org.readthedocs.build/en/4762/citing.html
• Project Overview/Conference Presentations: https://pygmt-dev--4762.org.readthedocs.build/en/4762/conferences.html
• External Resources: https://pygmt-dev--4762.org.readthedocs.build/en/4762/external_resources.html

Fixes #4746

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