A few updates to the About page

- Updated text on about-overview.png
- Changed about-typography, about-contrast, and about-modern-aesthetics from PNG24 to PNG8, saving 83 KB
- Reluctantly changed about-twentyfourteen from PNG to JPEG, because it saves a whopping 615 KB
- Tweak the headline size and styling of the about-twentyfourteen image to account for its lack of a transparent background.

See #26387.



git-svn-id: https://develop.svn.wordpress.org/trunk@26806 602fd350-edb4-49c9-b593-d223f7449a82