Text hierarchy styling tweaks

[fields37]

• [x] Change h2 size to 1.75rem, h3 to 1.4rem
• [x] Adjust spacing between them and mobile sizes
• [x] Add a p-small class, use for member bios and "last updated" line below table
• [x] Change member bio headers to both h4

[fields37]

Changes made in https://github.com/digitalcredentials/dcc-website-jekyll/pull/3

[kayaelle]

Thanks @fields37