* descriptions for getting started pages
* descriptions for layout
* add content page descriptions
* more descriptions, updates to some existing ones
* correct site url
* add social stuff to config for twitter cards
* add twitter meta tags; use large image for homepage and regular card for all others
* add the assets
* more site config
* more social shiz to partial, remove existing meta for the partial, remove page title from homepage for simpler if statements
Refs #19990
Continues the degruntification process.
Also removes mq4-hover-shim for now,
since it doesn't yet implement the standard PostCSS plugin interface.
- Simpler main nav on all pages
- Back to purple masthead on homepage instead of dark graphite
- Active link styles on the main nav
- Cleaned up sidebar nav
- New docs layout name
- Homepage copy edits
- Updated bright purple docs color